Think about the mission of the ASWB (and of the social work profession, for that matter). Social workers are helpers. They're helpers who are in a position to do some harm if they're not careful. So the powers that be want to give licenses to social workers who can demonstrate some basic understanding of how to help and, maybe more importantly, how to avoid doing harm.
What does that look like in an exam question? For starters, it looks like lots and lots of questions derived from the NASW Code of Ethics. It looks like vignettes designed to assess for social worker prejudice and bias. It looks like questions about scope of practice, making proper referrals, duty to warn, and such. Help and harm. After that, there will still be room for more general questions about theories and diagnoses. Expect to see the bulk of those questions focused on the basics: best-practice approaches (e.g., CBT) and diagnoses that social workers commonly see (mood disorders, personality disorders, psychotic disorders).
Getting the idea? There's a potential library to study, but what you actually have to get learned is much, much narrower. So crack open the Code of Ethics, sign up for some practice tests, and you're on your way. Good luck!