How to ask something like "what would you like to do?"

[fyp]

You can say 「なに聞きたい？」 along with 「なに言ってほしい？」 You can describe the situation to others saying 「（あいつ）日本語のナンチャラを聴きたがる」

I do feel that using a どう言えば～ permutation is more natural. I’d ask a child, for instance, 「なに聞きたいの？ Simple isn’t bad, either. 「晩飯さぁ、何がいいかな」is also a pretty common way to slice it.

At least in my experience.

[Kqaotix]

Might just be he’s correcting you because he likes doing it.
That’s quite the assumption.

And warning people against using tai alone when making declarative statements about other people wants (even in informal situations) seems like solid advice. But then of course, Japanese varies a lot according to area and age group and Japanese people often fail to take that into account as they’ve never had to study their own language from an outsider’s perspective.