I bought this (along with the law book) and used it to study for the NNPE, but I found that it's also useful as a practical guide to ethics and professionalism. The topics are clearly laid out and broken down into sections, and each topic is discussed with questions at the end. Some are open ended and meant for discussion, and some are multiple choice, with answers given.
The book doesn't indicate which topics might show up on the exam, to find that out you need to review the APEGA syllabus. The book is good for getting you to think about how you should approach problems, and how to answer the questions that come up. If you have the time, I would recommend reading the whole thing, if you're short on time, review the syllabus and study what you need to. You'll be missing out a lot if you do that though. It's genuinely one of the most useful textbooks I've read since my university days.