When Bran & team are at "The Gift" in a watch tower, there is a fight going on between Jon & Wildlings as Jon betrayed the Wildlings.
In this particular fight, Jon & Ygritte are fighting against 19 Wildlings, and during the fight, when a Wildling was about to attack Jon, Summer (Bran's wolf) attacks and kills that Wildling.
Why doesn't Jon recognize Summer? There wasn't any discussion about Summer after that in the TV series by Jon. Are there any references to this scene in the books?
He did in the books, though maybe not until after the event. Here is a quote from Jon I, A Dance with Dragons, where Jon is recollecting his siblings Direwolves,
At Queenscrown [where the fight and flight from the wildlings took place], one had come out of the darkness to save Jon’s life. Summer, it had to be.
They most likely left this out if the the TV series because of time constraints.
Edit/Added info for non-book readers: How Jon comes to this conclusion I am not sure. Initially, it seemed that he came to this realisation through the wolf dream (maybe with Ghost's better recognition of his brother). He could equally have used his human acquired knowledge that Summer's last known location was the closest of the direwolves.
From the same chapter, we see that Ghost knows Summer is now North of the wall (and hence was once close to it), Lady and Greywind are dead, Shaggydog is fighting Unicorns and Nymeria is alive. What is not clear is whether Jon takes this as fact or whether it just plays in his subconscious.
Summer
On the other side [of the wall] the wind was colder still, the wolf sensed. That was where his brother was, the grey brother who smelled of summer.
Nymeria and Shaggydog
Far off, he could hear his packmates calling to him, like to like. They were hunting too. A wild rain lashed down upon his black brother as he tore at the flesh of an enormous goat, washing the blood from his side where the goat’s long horn had raked him. In another place, his little sister lifted her head to sing to the moon, and a hundred small grey cousins broke off their hunt to sing with her. The hills were warmer where they were, and full of food. Many a night his sister’s pack gorged on the flesh of sheep and cows and horses, the prey of men, and sometimes even on the flesh of man himself.
Lady and Greywind Dead
Four remained … and one the white wolf could no longer sense [Summer beyond the wall].
Why didn't Jon recognize Summer?
Maybe he did but does it even matter? He thinks both of his younger brothers are dead at that time and he might have believed that Summer saved him by himself. Summer didn't even stay till the end of the fight, so Jon didn't really have the time to reconcile with the Direwolf.
One more thing to note is that Jon hasn't seen the grownup Summer before, he has only seen the pup, so there are chances he didn't recognize him. But from the show's perspective he never acknowledged it. And at that moment he didn't really have the time to either.
Since you ask for a books reference too: He recognized it was a dire wolf and also saw it was grey.
Ghost, he thought for one mad instant. Ghost leapt the Wall. Then the lightening turned the night to day and he saw the wolf standing on Del's chest, blood running down his jaws. Grey. He's grey.
But there were closer to 200 Wildlings, not 19, that night so Jon had to get away very quickly. The wolf saved his life (because Bran was nearby and was warging into him). Later when Jon was safely away he thinks
It was too large to be a common wolf. A direwolf, then. It had to be. He had never seen an animal move so fast. Like a grey wind ... Could Robb have returned to the north?
Jon V SOS.
In addition to the other excellent answers, I have one other aspect to offer -
Keep in mind, how did they initially come to get the direwolves? In the North, they happened upon pups and their dead mother. While surprised to find them that far south of the Wall, they weren't considered extinct or mythical (like, say White Walkers or dragons). Also, where the fight with the wildings happened was much farther north and probably closer to areas where direwolves might be more expected.
This would indicate that the Stark direwolves are not the only direwolves on the planet, and certainly not in the North. Since Jon, at that time, assumed Bran was dead and burned, he wouldn't necessarily think that Summer was even alive, let alone that any direwolf would have to be the same one. Also, when he last saw Summer, the direwolves were at a very different stage of their physical maturity. There wasn't any specific reason for him to make assumptions about the identity of that animal.
Good question. And luckily, this scene was adapted directly from the book.
At this point in the book, the wildlings had asked Jon to kill the old man. Jon hesitated, and Ygritte killed him instead. There is a giant lightning strike close by:
“And death leapt down amongst them.
The lightning flash left Jon night-blind, but he glimpsed the hurtling shadow half a heartbeat before he heard the shriek. The first Thenn died as the old man had, blood gushing from his torn throat. Then the light was gone and the shape was spinning away, snarling, and another man went down in the dark. There were curses, shouts, howls of pain. Jon saw Big Boil stumble backward and knock down three men behind him. Ghost, he thought for one mad instant. Ghost leapt the Wall. Then the lightning turned the night to day, and he saw the wolf standing on Del’s chest, blood running black from his jaws. Grey. He’s grey. Darkness descended with the thunderclap.
The Thenns were jabbing with their spears as the wolf darted between them. The old man’s mare reared, maddened by the smell of slaughter, and lashed out with her hooves. Longclaw was still in his hand. All at once Jon Snow knew he would never get a better chance.”
- A Storm of Swords - Jon V
Jon proceeds to fight his way out, and shortly after:
“Long hours later, the rain stopped. Jon found himself alone in a sea of tall black grass. There was a deep throbbing ache in his right thigh. When he looked down, he was surprised to see an arrow jutting out the back of it. When did that happen? He grabbed hold of the shaft and gave it a tug, but the arrowhead was sunk deep in the meat of his leg, and the pain when he pulled on it was excruciating. He tried to think back on the madness at the inn, but all he could remember was the beast, gaunt and grey and terrible. It was too large to be a common wolf. A direwolf, then. It had to be. He had never seen an animal move so fast. Like a grey wind … Could Robb have returned to the north?
Jon shook his head. He had no answers. It was too hard to think … about the wolf, the old man, Ygritte, any of it …”
- A Storm of Swords - Jon V
So in short, he simply never thought of Summer, but he knew it was a direwolf.
