Hi Tommino,
I would just call his flop check/raise and raise a good turn again to maximize your value.
As he didn't cap preflop he can't check/raise a lot overpairs here and a semibluff with just a gutshot is pretty unlikely too.
Board: 9d 8c 7h
Dead:
Equity Gewonnen UnentschiedenVerloren Hand
Spieler 1: 48.301 % 46.793 % 3.015 % 50.192 % JJ-77, ATs-A9s, ATo
Spieler 2: 51.699 % 50.192 % 3.015 % 46.793 % KhKc
Against this range you are only a slight favorite on the flop.
Board: Jh 9d 8c 7h
Dead:
Equity Gewonnen UnentschiedenVerloren Hand
Spieler 1: 88.851 % 85.197 % 7.310 % 7.494 % JJ-77, ATs-A9s, ATo
Spieler 2: 11.149 % 7.494 % 7.310 % 85.197 % KhKc
The turncard is very bad for you. I can see him donkbetting a lot better hands here as he may fear a check behind from you and may not to be 3-bet if he is check/raising as well.
Board: Jh 9d 8c 7h
Dead:
Equity Gewonnen UnentschiedenVerloren Hand
Spieler 1: 78.356 % 75.211 % 6.290 % 18.499 % QQ-77, ATs-A9s, ATo
Spieler 2: 21.644 % 18.499 % 6.290 % 75.211 % KhKc
If you add QQ you can make a crying calldown and as you can't be that sure about his range I like that the most. Maybe he openraised QJ instead of not capping QQ so as you can't be very sure here I like to look at his hand to get a better opinion about him.