ASWB's answer on aswb.org--depends if you're taking the exam before or after
January, July 2015. DSM-5 will start showing up then. Till then, the big, grey DSM-IV-TR is still the one to study.
UPDATE: Social Work Test Prep's been keeping tabs. As of April, the DSM-5 will start showing up on the ASWB exam in July, 2015. (Californians will see DSM-5 questions sooner--BBS exams will debut them in December, 2014.)