The phrase "What's he going to do?" is a common question in English used to ask about someone’s future plans or intentions. It uses the "be going to" future tense structure.
The general form for questions with "be going to" is:
Examples:
We use "be going to" to talk about:
A: Did you hear John got a new job?
B: Really? What’s he going to do?
A: He’s going to work as a software developer in Berlin!