"We are selling it"
It's Ji/Ma. I don't know if the hover hint tells you -- it does coming at the discussion from the sentences tab, but that gives info for the translation, not the question.
Ok, so that would be the default ngeli for a general "it" then. So then my question would be can't "it" be something already mentioned, and therefore belong to another ngeli? As in Q:"What are you doing with the table?" A:"We are selling it." It seems to me that more than just "Tunaliuza" should be accepted here.
I agree, but for Duolingo's purposes, I would use N/N agreement for unknown "it", as it seems to be the safest option. You should probably report it anyway, though.