It's called "The Promise" and is in three parts. It is mostly about how the idea of the United Republic formed, but there is a backdrop of Zuko trying to convince Ozai to tell him where his mother is. Ozai winds up just chastising Zuko, so Zuko sets Azula free to get the information. However, this is how the comic ends, and a new comic called "The Search" is set to come out this year that deals with Zuko, along with Team Avatar, looking for Zuko's mother.