Hi,
Just fold preflop, K9o plays horribly out of position and you'll just get into way more trouble than it's worth, for sure. We also have no read on villain except that nothing suggests he's a bad player so far.
On the flop I would check/call. If villain has nothing he will bet it on that board so we value from whiffed AQ that way. If he has a pair he's not going to pay off for 3 streets anyway on that board so it's not like we lose value if he decides to check behind the flop, we can still bet from the turn onward.
As played when he raises the flop that's when we regret calling with K9o preflop, because we're beat by every Kx hands most people show up with and since we're readless in rush we have no idea whether he's even capable of raising with diamonds or even AA there. So we're calling because we have trips and if we 3-bet most people will fold everything worse than that, but we're not thrilled about it.
On the turn I would just fold when he pots it. He might have the flush he might still have a better Kx, we have no idea if our "outs" to a full house are clean or if it'll only result in us splitting the flop. It's sad if he's bad enough to play AA that strongly without realizing he's just bluffing with it at that point, but I don't think it's worth finding out.
Hope it helps.