The majority of questions on the social work licensing exam aren't pulling for specific information about DSM diagnoses, developmental theories, and the like. They're vignettes that test for a core sense of social work values and ethics. How to prepare for those? The key reading is free, short, and just a click away: The NASW Code of Ethics. You've encountered it before, no doubt. As you're preparing for the exam, it's time to dig back in. It's worth rereading, word for word. And while you're doing that, you might pause with each section to imagine how the section might be tested for on the exam. Sometimes that will be obvious, sometimes less so.
Also valuable for preparing for ethics questions is Frederic Reamer's Eye on Ethics column from Social Work Today. Many of the dozens of columns contain their own vignette questions, exploring close-call situations that social workers often face. These closely resemble the very scenarios that you'll be asked to consider as you sit for the exam.