What chapter in bleach does yammy kill the doctor who fixed his arm?

You're likely thinking about the Arrancar Dordoni Alessandro Del Socaccio, not a doctor. He was the one who fixed Yammy's arm after it was broken by Ichigo in their first encounter.

However, Yammy didn't kill Dordoni. Dordoni sacrificed himself to save Yammy from Ichigo's Getsuga Tensho attack. This occurs in Chapter 203 of the Bleach manga.

Let me know if you have any other questions about Bleach!