Hello!
If villain is unknown, then my standard is:
Bet flop, check-fold turn.
Because:
1)They play in this limit way to much Aces (any ace rag, so they range is full of Ace) and if they hit ace on flop, they dont fold
2)They are overall passive loose in this limit, so i think, they dont bluff you out to much later, without ace, they check back often.
3)You are OOP, they dont fold ace, but they dont raise it also, so you dont know your hand equity
4)KK is nice hand, but here its 2nd pair.
5)There is no draws out - it means he have strong flop callingrange overall.
I think they check back with Tx, 88 and hands like this.
So if you check, and he bet, fold, you cantcall, because you are OOP and you see really often in river also bet, its cost much money to you.
If you check and he check back, then i like bet half pot, because:
1)value against Tx, 88 and hands like this, if you check, he may check back, you lose value
2)you put price, he cant really raise you with weak ace, but if you check, he defenetly can bet more than half pot, if he have ace and i think you should call then.
3)NL5 are very passive overall, they dont do pure pluffs, so if you bet and he raise, i fold here, he have stronger hand, but if you check, he bet this hand anyway and you must call, you waste same amount/less money anyway against this range, but by betting yourself you get value against other hands also.
As played fold river.