Synchronization is the focus of quiz 8. You should be able to explain, in the context of a concrete example, how access to mutable data is a problem in the absence of synchronization. You should also understand very basic issues with wait(), notify(), and notifyAll(), at least in the context of the examples given in class.
You should also have read Bloch's concurrency chapter (Items 66-73). Although there is a lot of material in this section, general questions are fair game.