what is the joke that ross and chandler fight about in “the one with the joke”???

Chandler: So Steve said he had to go to the doctor. And Steve’s doctor’s name is Doctor Muppy. So I said, ‘Doctor Monkey?’ And that is how the whole Doctor Monkey thing came up. (He slams his feet up on the table to emphasize his point.)

Ross: Are you kidding? Okay, look. I-I studied evolution. Remember, evolution? Monkey into man? Plus, I’m a doctor, and I had a monkey. I’m Doctor Monkey!

Chandler: I’m not arguing with that.

Monica: All right, I’ve heard enough. I’ve made my decision.

(Both Chandler and Ross are eager to hear her decision.)

Monica: You are both idiots. The joke is not funny, and it’s offensive to women, and doctors, and monkeys! You shouldn’t be arguing over who gets credit, you should be arguing over who gets blamed for inflicting this horrible joke upon the world! Now let it go! The joke ꜱᴜcκs!

so they never really say what it is, but its about a monkey and a doctor or something like that

A woman goes to the doctor.

The door says “Dr. Monkey”.

The woman enters and asks: “Doctor, I feel very ill lately. Do you know what I can do?”

The doctor answers: “I ll write you a prescription for what makes me feel better - Sucking on a banana.”

Dr Monkey Joke

Ross shows the gang his joke that was published in Playboy magazine. When Chandler reads it, he claims the joke is his and Ross stole it from him. Since Playboy does not print the submitter's name, Chandler and Ross continue to fight over the joke, each claiming that they are the real author. Ross and Chandler leave it up to Monica to decide who wrote the joke by hearing each of their sides. When Monica tells them she doesn't understand why either of the would want credit for writing such a horrible joke, they begin to argue that the other wrote it. Joey has become increasingly strapped for cash since Janice moved out. Gunther offers him a job at the coffeehouse, but Joey is reluctant to take it because he would have to wait on his friends. He ultimately takes the job and attempts to hide it from the group. Meanwhile, the girls discuss which one they would want to date out of the three. Phoebe makes the mistake of picking Rachel because Monica is high maintenance and Rachel is more of a pushover. They take offense and try to get Phoebe back by calling her flaky.

I think bella just answered your question you go girl lol