How does Thanos know where all the infinity stones are?

Question

In Avengers: Infinity War it seemed to me that Thanos (somehow?) always knew where the infinity stones were (except for the soul stone). Like he was using the space stone to get himself/teleport to the other stones' location all the time.

How does Thanos, conveniently, know where all the other infinity stones are, so he can go to that location?

Edit and clarification:
It's nice to see answered how he knew general location of the stones, but I was thinking more of how he knows exactly where they are.

For example (and as per answers):
He knows that Loki has the Space stone, but how does he know that Loki is in that spaceship?
He knows that the Time stone is on Earth, but how does he know that it is in New York?
He knows that the Mind stone is also on Earth, but how does he track Vision (in Scotland?) ? He even tracks him somehow when they take him to Wakanda. How?
Those were the things I meant when I said he knows where the stones are.

Answer 1

Quite possibly because he orchestrated things so that the stones would be revealed.

At the end of Age of Ultron when Thor is going to leave he says:

Thor: I have no choice. The Mind Stone is the fourth of the Infinity Stones to show up in the last few years. That's not a coincidence. Someone has been playing an intricate game and has made pawns of us. But once all these pieces are in position...

Source: Transcripts Wikia > Avengers: Age of Ultron

consider also that it was Thanos which gave Loki the Staff which had the Mind Stone in it and had hired Ronan the Accuser to find Power Stone, or at very least the Orb know it was in it

Ronan: I promised Thanos I would retrieve the orb for him. Only then will he destroy Xandar for me. Nebula, go to Xandar and get me the orb.

Ronan: The orb is in my possession, as I promised. [Korath holds up the orb in his hand]
Thanos: Bring it to me.
Ronan: Yes, that was our agreement. [Ronan takes the orb from Korath] Bring you the orb, and you will destroy Xandar for me. However, now that I know it contains an Infinity Stone, I wonder what use I have for you.
Thanos: Boy, I would reconsider your current course. [Ronan opens up the orb and looks at the Infinity Stone inside]
Korath: Master! You cannot! Thanos is the most powerful being in the universe.
Ronan: Not anymore. [suddenly Ronan embeds the Infinity Stone in his warhammer and absorbs its power into his body] You call me "boy!" I will unfurl one thousand years of Kree justice on Xandar, and burn it to its core! Then, Thanos, I'm coming for you. [he ends his call to Thanos]

Source: Transcripts Wikia > Guardians of the Galaxy

also in Avengers: Infinity War it's revealed that:

Thanos had sent Gamora out to find the Soul Stone and after capturing and torturing Nebula, learned that she had found it

while Power and Mind is easily explains we don't exactly know exactly how he knew where the Space Stone was at the time he sought it out or that the Reality Stone was at Knowhere in Taneleer Tivan's possession but given Thor's statement in Age of Ultron he may have orchestrated things in some so that he could find them more reliably as oppose to having had the Tesseract left on Earth and the Ether hidden away by Odin's father, Bor Burison.

as for the Time Stone, while we don't know if he had any hand with the Eye of Agamotto ending up in Kamar-Taj however i would suspect that he or the Black Order knew that either:

a) Attacking the New York Sanctum would lure out Strange with the Time Stone

and/or

b) One could get to Kamar-Taj from the New York Sanctum as the Black Order landed in New York rather than Tibet

there is also the possibility that the Stones react to one another as they come together as:

Vision's Stone start to react with him commenting that it was trying to warn him and Thanos only needed a couple of stones, the ones he knew where they were, in order to find the rest. however this might have been a unique property of the Mind Stone as Thanos still needed Gamora to reveal to him the location of the Soul Stone

Answer 2

Thanos is, and has been for some time, gathering information on the stones and their whereabouts. He's shown to have asked Gamora to locate the Soul Stone for him, and it stands to reason that he has asked either her or others in his employ to locate the rest of the stones.

Given that it's his "destiny" to control all of the stones, he will have made it his business to know everything about them and where to find them.

He knew the Power stone was on Xandar - he knew that was where Ronan had taken it and lost it to the Guardians of the Galaxy.

He knew the Collector had the Reality stone, though it's unclear exactly how he found that out. He did get it after the attack on the Asgardians, so perhaps he got that information through torturing them.

He knew the Mind stone was on Earth - he gave it to Loki to take there, in order to try and gain the Space stone. He was aware in the aftermath, that the space stone went to Asgard.

It's not entirely clear how he knows where the Time stone is, but the Eye of Agamotto has been with Earth's Sorceror Supreme for a long time (The Ancient One before Dr Strange), so it's entirely likely that it's generally known where that one is.

Answer 3

Through Ronan and Loki, Thanos at least has a good guess to the location of all but the soul stone.

He spent many years hunting down the stones and his desire to achieve his goal is what led him to forge deals with Loki and Ronan the Accuser in their respective campaigns against Earth and Xandar, as seen in his promising to aid them in exchange for an Infinity Stone. Both of these new alliances cost Thanos much of his resources, including one of the stones and the loyalty of his two daughters, Gamora and Nebula, and inadvertently resulted in the formation of the two superhero groups: the Avengers and the Guardians of the Galaxy. Fed up with these failures of his subordinates, Thanos opted to seek out the six Infinity Stones himself.

Ronan informed Thanos that he has The Orb (the power infinity stone) and that he’s going to Xandar with it based on his quote. That’s the first stone that Thanos recovers before Infinity War starts.

"I will unfurl one thousand years of Kree justice on Xandar and burn it to its core! Then, Thanos, I'm coming for you!” Ronan the Accuser to Thanos

It’s reasonable for Thanos to assume Loki may have the Tesseract based on the events in the first Avengers movie and Thor Ragnarok. We see he’s right at the start of Infinity War.

In 2012, after his defeat at the hands of Thor, Loki came into contact with the alien race known as the Chitauri, and their master, Thanos, who had already been seeking the Tesseract. Loki promised to retrieve it from Earth and give it to Thanos in exchange for his army. Through manipulation of the Tesseract's energy, Thanos teleported Loki to the Tesseract's location at the Joint Dark Energy Mission Facility.

When Loki went into Odin's Trophy Room to retrieve the head of Surtur, he passed by the Tesseract and took it from the vault.

I’m not sure how Thanos identified the Collector as having an infinity stone; but I would suspect the Collector in his own hunt for the other stones was not as careful as he should have been.

Once Malekith was defeated, the Asgardians managed to contain the Aether and, with the Power Stone already in their possession, feared having too many Infinity Stones in one place. Instead, they gave it to the Collector, who promised to look after it – not realising he intended to collect them all himself.

Given the failed invasion of New York and that Loki doesn’t have the scepter, Thanos can assume that the mind stone is still on Earth.

Thanos also provided Loki with a Scepter containing the Mind Stone.

It’s possible that Loki, Kaecilius or Dormammu conveyed to Thanos that the time stone is on Earth. Or given how long the time stone has been on Earth, Thanos could have known about it for centuries.

Strange wore it once again a little while later while meeting with Thor and Loki.

Thor’s vision is what makes me feel Loki had the knowledge about the time stone.

I won’t say I know completely how; but I will say Thanos had means of gaining this information.

Even if it isn't well explained, by the end of Avengers: Age of Ultron, it's clear what Thor learned. He's the first person to connect the gemstone dots.

Answer 4

This can easily be answered by a line in Guardians of the Galaxy.

The Other talks to Ronan and tells him that Thanos' sources have revealed Gamora's plans to sell the Orb.

This tells the audience that Thanos has spies and agents throughout the galaxy keeping tabs on things.

In Age of Ultron he decided that instead of staying behind and just having his minions bring the stones to him while he sits on his throne, he would join the hunt himself. Before getting the stones however, he wanted to make sure they were all attainable first. This is why he waited until Nebula revealed that Gamora knew where it was. Once he knew where all of them were, then the hunt would begin. Whereas before having his minions take them forehand would've been a problem for two reasons

1). What if all six weren't able to be found, which was the case until the Soul Stone's location was revealed. Then his quest wouldn't have mattered since he can't attain all of them.

2). Having his crew hunting for them early on without him proved to be a failure as the last two time where he had someone else fetch the stones without him at their side, they failed. Whereas now, with him joining the hunt as we see in Age of Ultron where he says "Fine, I'll do it myself", it will increase his chances of completing his goal, now that he's actively participating.

He knows the Mind Stone is on Earth because of Loki's failure when using it during Avengers 1. He sent Proxima and Corvus to track the stone down, which they did, until Vision escaped, and they tracked him down to Wakanda by keeping tabs and following him.

The Power Stone, he knows Ronan took it to Xandar and it was being kept by the Nova Corps.

Soul Stone, he knew Gamora knew the location and forced her to tell him.

Time and Reality Stones, since he has spies and agents keeping tabs on the stones, he could've found it on Earth/Knowhere because of that. It's also possible that he could've tortured that info about the Reality Stone from Thor, since he knew where it was.

Space Stone, Thanos knew it was taken back to Asgard, and once the opportunity presented itself (once he knew where ALL of them were) he went there only to find Asgard destroyed, and he tracked down Thor and Loki's ship.

There's also one thing to keep in mind. The stones are actually alive, or at least have some form of sentience. They communicate with each other, which is how Loki teleported to Earth in Avengers 1, he used the Mind Stone to communicate with the Space Stone and allow him to instantly teleport to Earth. [EDIT - It wasn't the stone that did this, but Loki mind controlling Selvig to build a machine to do that.]

Same with the Tesseract in The First Avenger. For abusing the Space Stone's power, the stone banished Red Skull to Vormir, and it communicated with the Soul Stone in order to transport him there.

In Age of Ultron Bruce and Stark discover the Mind Stone is sentient, and want to use it's power to create Ultron.

Plus, the Soul Stone requires a sacrifice of what you love, Red Skull even says that the Stone itself demands a sacrifice. Plus Red Skull referred to the stone as "Soul" and that it has "a special place among the Infinity Stones. You might say it has a certain wisdom." He's personifying the stone. This further shows how the stones are alive and not just objects

I bring this up because in the scene where Thanos states in Infinity War, "There are two more stones on Earth" the Space Stone was glowing, which indicated he was using it.

Answer 5

I think he either knew where they were when he had the mind stone originally before giving the scepter to Loki. May be the mind stone told him the whereabouts?

Or, some of the mind stones have energy signatures and he was able to find them with long range sensers/detectors. Maybe some of his children knew like Ebony? He had telekinetic abilities.