HI,

So this hand is played on site which allows no poker tools/softwares and no info about villain, played with him 2 orbits so far and he seemed very fishy.

Villain limps utg sb completes i check j966ss on the bb.

Flop t85 with fd i dont have, utg limper pots 1.5bb sb folds i call. Turn is offsuit 4, and villain again leads with pot. I decide to raise with my blockers to about 18bb and villain thinks for a short while and calls.
Then river is a offsuit 4 so board is t8544 there is no flushes, there was one flushdraw ott where villain called our potbet. So now im in a weird spot becouse i feel like i cant rep much on that river if i bet. Villains pot/call ott seemed pretty weird also with any real hand like 2p + becouse why would he lead on that turn when it looks very scary for him after i call that flop, and hes range has to be towards draws i think.
So in a vacuum after villains turncall on that river is the best play to check or a bet? And what if we have like nines or jacks compared to sixes as a real hand?

If you're saying he's "very fishy" then you need to define what characteristics he has that support this, so that we can use that to exploit him.

Does he call way too much with weak draws or weak hands? Does he fold way too much and give up the best hand or large portions of equity? Does he seriously overplay hands and get it in with trash?