UTG (Hero): $5.00 (100 bb)
UTG+1: $5.65 (113 bb)
MP: $4.78 (96 bb)
MP+1: $5.13 (103 bb)
LP: $2.00 (40 bb)
CO: $5.68 (114 bb)
BU: $2.67 (53 bb)
SB: $11.77 (235 bb)
BB: $4.95 (99 bb)

Pre-Flop: ($0.07) Hero is UTG with K♠ K♥
Hero raises to $0.15, 1 fold, MP calls $0.15, 2 players fold, CO calls $0.15, BTN calls $0.15, 2 players fold

Flop: ($0.67) 6♣ 4♣ J♥ (4 players)
Hero bets $0.50, MP folds, CO calls $0.50, BU folds

Turn: ($1.67) 8♥ (2 players)
Hero bets $0.55, CO raises to $1.50, Hero calls $0.95

River: ($4.67) J♠ (2 players)
Hero checks, CO bets $2.33, HERO?

Villain is 10/5/1 (VPIP/PFR/3B), 320 hands, no additional reads.

My line of thinking is as follows: -

Flop bet standard, we get value from all J and all FD. Villain have a lot of Jx hands, some sets of 4,6 and some Ax flush draw.

Turn bet is perhaps smaller than optimal but Pio seems to think the EV doesnt change much whether betting 33% or 75%. With the rereaise I think with KK is an obvious call here, although it's strange that PIO also advocate raising KTs, ATs.

On the river, this size is almost equivalent to a shove, we need about 25% equity and defend at least 67% of our range - but I personally find it hard to call and be ahead here against villain's tight range.

Not too sure what to do here, I put the same range of 10% into equilab and KK has about 78% against his range, however given the turn reraise, even if he did it with KJ/AJ, I would be beat here. I'm not confident that he has any bluff here, except maybe something random like AThh?

I guess my question is, am I too nitty if I fold here or is this a spot where we just sigh and call to remain unexploitable? Or if my understanding is wrong please correct me.

I think your thinking is correct, are you really using PIO at 5NL?

My main advice is don't worry about being unexploitable when playing a 10/5 nit. He certainly isn't worrying about it, and isn't exploiting you.

Yeah, actually I'm just trying to build my roll and simulate live environment somewhat since I sometimes play 1/2 or 2/5 depending on game availability and it's frustrating sometimes I don't know what to do without a HUD so I started learning GTO and ppl tell me about PIO so i got the free version as well

Free version makes for sense, ive not tried it, can you do much with it?

unfortunately you can only see turn actions and stats, so not entirely useless but of course by turn usually ranges are more linear i think? I'm thinking of getting GTO+ so at least i get to learn about different board texture.

Do you use anything of the sort?

I don't yet, I recently got back into poker after a long while, haven't seriously played online since 2010. Started at 10NL and working my way up, but solvers etc are all new to me. I figure if I get to 50NL it might be worth getting one, but until then I think other study methods are probably more efficient from both a time and $ perspective.