Could you please tell me the meaning of "get on me" in the following excerpt from the Chapter Two of The Great Gatsby? Does it mean "to learn something against me"?
“I’m scared of him. I’d hate to have him get anything on me.”
This expression can have only one meaning. You are quite correct in assuming that it means "to learn something against me." It would be more accurate to say "to learn anything that he might be able to use against me"--or even to set her up, to get her to do something illegal that he might use against her or use to force her to do more illegal acts for him. Maybe Catherine is actually a bit thrilled by the imaginary possibility.
It is Myrtle's sister Catherine who confides to Nick regarding Gatsby:
"I'm scared of him. I'd hate to have him get anything on me."
She has only been to Gatsby's once at one of his parties.
"I was down there at a party about a month ago. At a man named Gatsby's. Do you know him?"
He wouldn't even remember her, and it is hard to imagine anything this insignificant woman might have done that Gatsby could get on her or want to use against her. The worst thing she ever does is to drink liquor during Prohibition, and she probably knows a few bootleggers. She doesn't sound as if she actually met Gatsby at that party. She is probably "scared" of him because of all the gossip she heard about him that night. People at those parties repeat all sorts of rumors about their host. They would like to think that he is an outrageously powerful, wicked, and colorful man because it would make them feel important to have been at one of his parties, to have seen him in person, and perhaps even to have been introduced to him.
If Gatsby actually "got" anything on Catherine and wanted to use it against her, he would not go through legal channels. He could probably pass his knowledge on to some hoodlum who might want to take revenge for something she had said or done. But Gatsby has infinitely more important matters to think about. Catherine would just like to think she had some importance. She is like a lot of people who were thrilled by being petty criminals and knowing petty criminals during the Prohibition era. They liked going to speakeasys and seeing dangerous characters at nearby tables. Some mobsters such as Al Capone were widely admired. Breaking the law was fun, and big-time lawbreakers set the tone.
Gatsby himself was hardly a typical big-time mobster. He is a anomalous character because he tries to act like a perfect gentleman, an "Oxford man."