Oh I've read the book and it clearly influenced the TDK Joker. Jonah Nolan has gone in depth about it in interviews. The Joker attempting to push one of Batman's allies over the edge into madness is a common plotline between Killing Joke and TDK. Joker's multiple origin stories in TDK are a nod to his amnesia about his origin in Killing Joke. The first book Nolan gave to Ledger for researching the role was Killing Joke. The Barbara Gordon sequence you mentioned is an example of how Ledger viewed the Joker. While he prepared for the role, he kept a journal with things the Joker would laugh about, which included rape, AIDS, nuclear war, and so forth. It shows up in the movie too. Ledger's Joker had the balls to kill Batman's love interest, whereas Jack's Joker fell in love with her.