Where did Gamora find the Map to the Soul Stone in Avengers: Infinity War? On her planet or on Titan or elsewhere? At that point does she travel to Vormir without Thanos' knowledge? How does she know where on the planet Vormir to take Thanos when they visit together if she only assumes the map she found is true? Did she previously meet Red Skull? How was she certain the stone was there otherwise?
We don't know!
There is no explanation given as to how Gamora locates the map or the location of the Soul Stone, she just announces that she does know.
The locations of the various stones is purely an MCU construct, there is no equivalent in the comics which have a somewhat different structure than the movies.