Villain is unknown only have 14 hands on him. If he has a K then I want to bet but if he called with a flush draw then hmmm. I guess KJ is also possible. How to play the turn should I bet or check?

Party Poker
No Limit Holdem Ring game
Blinds: $0.10/$0.25
9 players
Converter

Stack sizes:
UTG: $5.50
UTG+1: $5.15
MP1: $5.55
MP2: $24.65
MP3: $23
CO: $16.45
Button: $40.16
Hero: $26.47
BB: $3.75

Pre-flop: (9 players) Hero is SB with A K
5 folds, CO raises to $0.75, Button folds, Hero calls, BB folds.

Flop: K 3 7 ($1.75, 2 players)
Hero checks, CO bets $1.5, Hero raises to $4, CO calls.

Turn: J ($9.75, 2 players)
Hero???