Umm you can't use the reasons: "he'll call with one pair hands which I beat." and "He'll fold weak 2 pair hands which beat me." together as they are never both true at the same time. If he's not calling with the Qs in his range the jam is terrible regardless of whether he occassionally folds Q9.

In actuality, I doubt he ever folds two pair and proabably never top pair either having invested this much already and it being 2NL and him being an evidently massive fish.

If he does this with top pair then this seems fine because yeah I agree he'll likely call it off with these hands and draws too for the same reason as I stated above. Idk what 2NL donks typically do, but at 25NL and 50NL, with passive fish, this line is usually a stronger range than you've allocated this guy.

Given that his range is so wide prelflop and he'll never fold draws or top pair, I'd probably go ahead and just 3-bet the flop for value since we have good equity vs his stationy felting range.

Btw, he isn't "donking to you" on the turn. He raised the flop, therefore he has the lead. A donk out is when he calls your flop bet and then leads the turn.