Would this book just cover only the topics asked in the exam?
We like to say we cover 115% - hopefully that's the case. So we cover what's on the exam, plus a little bit extra.
Would you cover all the topics available in Java 8 - like a quick reference guide for the Java 8 changes or topics?
Definitely not; we really focus in on the objectives for the exam and everything we cover is related to those topics.
Would you cover the topics in the beginner perspective or advanced too?
I'd say we cover the topics from an intermediate perspective; we do assume you've been programming in Java--hopefully you're not taking the exam as a newbie Java programmer--but we try to cover the topics we do tackle in a way that you can learn it if you haven't come across that language feature before.
Hope that helps!