$200NL pokerroom.

Just came to the table, no reads.
Very first hand. Hero had $200 chips, Villain had $100.

Preflop
Villain (UTG) raises to $4, 4 folds, MP+1 calls, 2 folds,
Hero (BB) 4 8 calls.

Flop ($13) 9 J K
Hero checks, Villain bets $5, MP1 folds, Hero calls.

Turn ($23) 7
Hero checks, Villain checks.

River 6
Hero?

Without a read I think you have to bet this turn. You can't give him an opportunity to draw to a higher flush.

I don't get it
Why are you caling a raise with 48 and calling the flop bet if you aren't betting the turn?

Or were you looking to c/r?

Are you now asking "How much to bet no the river?"

I'll say: $10-15. But I'm not too good.

I think this must have been the case.

As for the river... I think 3/4 of the pot should do the trick.