Mometrix offers online counseling- and social work-related study guides including practice questions for the ASWB Bachelor's, Clinical, and Master level exams and a number of other exams. The social-work-related list is available here.
The ASWB "is the nonprofit organization composed of and owned by the social work regulatory boards and colleges of all 50 U.S. states" and other states. It facilitates the licensure exams.
The Practice of Generalist Social Work by 
Social Work ASWB(r) Advanced Generalist Exam Guide by