What does nick learn about jordan baker after he has spent some time with her?

Nick learns that he is very attracted to Jordan Baker BUT Jordan is extremely cynical, with a masculine, icy demeanor that Nick initially finds compelling. The two become briefly involved, but Jordan rejects him on the grounds that he is as corrupt and decadent as she is.

He learns that she is compulsively dishonest, and that she cheated to win her first golf tournament. She assumes that everyone else is as dishonest as she: she automatically concludes that Gatsby's books, like the better part of her own personality, exist merely for the sake of appearance.

that she is compulsively dishonest