This spot is difficult because with him being an unknown we don't really have any range of hands to put him on. We are getting good odds here but I think that I would still fold this. Most of the hands we are beating aren't going to bet this turn, and the jack definitely improved a lot of the hands that we were beating on the flop. I'd be concerned that if we call here then we are still going to get bluffed off of a lot of rivers.

 I kinda like a check on the flop assuming villain thinks we might c/r Kx sometimes.  I'd take a guess at the leveling game and usually fold turn (else call, call river).