Dr. Ismail Ak lives in Turkey. But Cho could have come across the name by doing Internet or library research, e-mail correspondence, etc., on the types of issues that evidently affected him.
WaPo now reporting that it was actually “Ismale Ax” tattooed on his arm. However, this might still be related to Ismail Ak since it could be a play on his name or his nickname for him. If it does turn out to be Ismail Ak then it must have been a powerful connection to actually have the name TATTOOED on the arm.