"Who is your lawyer?"
Translation:Cé hé do dhlíodóir?
atá is a form of the verb bí. This would be a copular question, so you'd need hé (or hí) after cé. It literally translates as "Who is it, your lawyer?"
Would cé hé or cé hí be used for all copular single person "Who is..." questions, then?
My bad. I misread it as just "who is..." questions.
For copular ones, yes. At least in the standard. In Connacht Irish, you'll see Cérb é for 'Who is he' (Cérbh é in the past).
I don't we've actually learned anything about hé yet. And yet here it is in review.
That’s how DL works. It by and by introduces new material mixed into stuff already learned so that you can draw your own conclusions about what’s going on. Not every single aspect of complex grammar can be dealt with in the sparse notes that DL offers. They give you the very basics; the sentences provide a variety of usages.
Apart from that, we have encountered the h affixed between to “colliding” vowels previously, e.g. Dé hAoine. So this is only a new variation of an already learned mechanism.