My award ticket s issued by AC. I also saw TK doesn't have a transfer desk at hkg.
Flight to IST is a layover with onward travel to us. Typically I've needed to checkin at airport whwn travelling to us due to document check for other airlines.
Since TK uses sq lounge could the lounge agents checkin / issue boarding pass? Not sure if it'd be too risky to wait to check in at the gate