Question

Nobody wants to talk about it? (doesn't he) (do they?)

Answer 1

Nobody wants to talk about it, do they?

В английском языке неизвестное лицо (например, "he or she") — это всегда "they".

Answer 2

The correct phrasing would be "Doesn't he want to talk about it?" or "Does he not want to talk about it?" for a singular subject. For a plural subject, it would be "Do they not want to talk about it?"