I don't know about J class but I flew many times from the US to Turkey with TK. The planes are usually Airbus 340. So, seats and pitches should be like any other Airbus 340, me personally had no complaint whatsoever. (One forum member commented here that seats are hard ???)
Service and food (especially the Turkish Wine) is exceptionally good, FA's are nice and polite. If you are flying from JFK, TK is stationed at Terminal One, which is probably the best terminal building of that airport.
I definitely recommend TK to anyone flying to Turkey.