One of the meanings of the adjective due is "expected to give birth", another one is "expected according to timetable, promise etc."
The context:
A: I saw Jane just the other day. Seems like you're going to become a father soon.
B: Yes, and it's going to be a boy!
What question may one ask (using "due) about the approximate time (months or weeks) when the childbirth is awaited?
Would it be about the baby boy expected to appear:
When is he due?
Or about the mother expected to deliver the baby:
When is she due?
What may be other most common questions (just a couple of them) to ask the father-to-be about the same thing.