"Is he a doctor?"
Translation:An dochtúir é?
Figuring out the difference between bí and is and where to use each is half the fun of learning Irish? Where else could you have this much fun?
Only if you did something like An bhfuil sé ina dhochtúir. Otherwise, you need the copula structure.
I used "an bhfuil sé ina dhochtúir?" and was marked wrong. Should be correct, shouldn't it?
An é an dochtúir? or An eisean an dochtúir?
(Gramadach na Gaeilge suggests that the emphatic eisean should be used rather than the plain é, but that really depends on the question you are asking. If you are asking which of the different people in front of you is the doctor, eisean makes more sense, if you're trying to find out what the profession of the person you are taking about is, é is better).