What is the turning point in the novel?It seems like there are multiple turning points, but i need to choose only one.
You certainly have a wide range of choices.
I would probably pick one of the following:
When Mr. Antolini (if I am remembering correctly) comes out of his bedroom and touches Holden's head and Holden freaks out. At this point he had begun to trust him a little bit and felt like he was actually in a safe place, but then his paranoia kicks in really hard again and he is off and running mumbling about how everyone is a pervert or a phony.
The interaction between him and the prostitute and then her pimp. I don't think Holden ever intended to sleep with her, but it brings him so close to the contradiction in the way he views himself and his actual self that you might say he really falls off the cliff afterwards.