"Who is his child-in-law?"
Translation:ʻO wai kāna hūnōna?
Truthfully, I would accept either though I would encourage haumāna to use A class for this relationship. But the reason kona is accepted right now is because there is a bug in the Duolingo system that allows it to be, I suppose because it is only one letter off. It has not been listed as an accepted answer by the Hawaiian team.