Be careful with the book you have bought. Some of the answers/explanations given are not correct or will be at odds with the JAR answer to the same question. It's a useful tool to swot up quickly and highlight the areas you are most rusty in, which is when you should dust off the ATPL manuals and get stuck back into the problem area.
Each airline has it's own pet subject, so look at the a/c type and routes and make an educated guess as to what they may ask. I would suggest the vast majority of questions will be met, POF and performance related, with some systems (although as this can be too type specific it might be less likely).