What kind of scene described in the novel (including a quote) would be best to use?

Take your pick.  There are plenty of scenes that speak
volumes.  You could go with something seemingly ordinary, such as when Holden opens
Chapter 3 with "I'm the most terrific liar you ever saw."  This line speaks volumes
because it is part of his development. He lies simply for the freedom of it; to be free
enough to lie, to be unaccountable, and in general, to be hidden from anyone he doesn't
want to be around.  We get the impression that he lies only to "phonies" because they
live inauthentic lives and wouldn't know truth anyway.  But he also lies because it
sustains his feelings of alienation (which, ironically, he shares with the nuns.) 
Holden is a skeptical truth-seeker in that he thinks most people are phony, but still
looks for truth or something good even though he can't quite decide if he does good
things or selfish things.  His overwhelming skepticism of the world justifies (to him)
his behavior.  And it's not really elitism.  Holden's self-isolation is also a way to
not be corrupted by the phonies of the world; and yet he wants or needs to connect with
people (Phoebe for example).  Hence, his desire to be a catcher in the rye (Chapter 22),
perhaps saving others like himself from becoming phonies (adults).  But this is also
part of his nature; is it selfishness or virtue to want this?  Or is it
both?