Not exactly a spot that'll come up too often but thought it'd be interesting to get people's opinions none the less. There isn't really a standard line on any street, so wwyd differently pre to river?

Opener is a fish playing 59/34 and hasn't made a 4bet. This fish is super LAG, and seems to have somewhat of an understanding, so wont be simply cold calling 4bs for fun.
3Bettor is a weakish reg, who 3bets 10.9, folds to 50% of 4bets over a large sample and won't be getting in QQ with me pre i really dont think.

Can post more post flop stats on demand as im not 100% on what is relevant, but here is how I played it:

Ongame Network $1/$2 No Limit Hold'em - 6 players - View hand 1670466
DeucesCracked Poker Videos Hand History Converter

SB: $453.85
Hero (BB): $431.68
UTG: $214.05
MP: $296.80
CO: $386.95
BTN: $290.00

Pre Flop: ($3.00) Hero is BB with K K
1 fold, MP raises to $6, CO raises to $18, 2 folds, Hero calls $16, MP calls $12

Flop: ($55.00) 6 8 9 (3 players)
Hero checks, MP checks, CO bets $41, Hero calls $41, MP calls $41

Turn: ($178.00) K (3 players)
Hero bets $94, MP folds, CO calls $94

River: ($366.00) 8 (2 players)
Hero bets $278.68 all in, CO folds

well given your thoughts, pre can't be played any other way.
I think donking OTF has some merits as reg will be checking a huge portion of the time. Well as played, yeah probably donking OTT is the best decision since on such card (actually doesn't really matter what card comes here) reg will be checking again a lot since you show strength and unless he has aces - he's afraid of being behind of you. I think a slightly bigger donk would be better, like ~110$.
What's the remaining stacks OTR? I'm asking cause I'm not sure I like your sizing, it puts too much pressure on reg

Line is okay, but lead turn bigger (like $115) to set up stacks better.

Donk flop ainec.

Pre seems good/standard.

On the flop I much rather donk, and probably folding if any of them raises. Reg checks a lot on this flop, probably just betting KK+ and stuff like AcKc, KcQc,... And we can't rely on the aggro fish to bet here (unless you have some solid read).

As played I like the turn donkbet, just make it bigger for value, to charge more on the draws, to set up a less scary river shove,..

where did TT JJ QQ go?

Would like to 4bet for value but if you really think they are just folding then flatting is fine.
Donk flop. Play it like a normal overpair in a multiway action flop. CC leaves you guessing too much on too many turns without the initiative.

Anybody check river? Doesn't have villain have far more hands to bluff with than to call with?

What other hands do we donk on the turn in this spot besides KK? Are we even balanced?

doubtfully we need to be

checking river wont give more value than betting in the long run, his range is exclusively PPs and he has a decent amount of SDV - i dont think he will turn them into a bluff more often than just **** it i must call

donkbet/broke flop ainec +1
bet bigger on turn +1
pre is ok because i see a lot of AJ/KQ 3betting here for value/to isolate and of course it's more fun when the fish comes along, but i think you're wrong if you say someone with 10.9 3bet range won't shove a cold 4bet with AK/QQ, unless you're really really nitty.

I think that, as played, once we c/c the flop we should check the turn too.

Mainly because we look so ridiculously strong after cold-calling an MP 3 bet OOP, c/c a large cbet on a wet flop 3 way, and then donking this turn card. If villain has half a brain (which presumably he does since OP described him as a reg) he’s going to be folding all his bluffcatchers to this line and we’ll only get value vs. hands that would DB anyway. We also at least give him the opportunity to bluff- both with air hands (very unlikely given flop play) and weaker one pair hands he was betting for value with vs. the fish (9x/88/TT etc.)- since he’s likely to weight our range quite heavily towards TT-QQ at this point.

The only real advantage I can see donking the turn having over checking is protection, which is admittedly quite a significant concern on this board texture, but probably not enough to sway the decision that way.

Forgot to add this point and can't edit now, but he can also conceivably bet QQ for value/protection OTT for this reason, whereas he will very likley fold that hand if we donk $100 or w/e.

On his situation, if I have TT-QQ I'm never betting on the flop. Chances are that 3b coldcaller has KK+ a lot of the time. Tbh this is mostly true with 100bb eff stacks. As I don't play deep games much, I don't know what people coldcall a 3b with on this specific situation.

i didn't see how deep we were, we can't go broke on this flop