When the objectives mention "wrapper" classes, it's referring to the the primitive wrappers eg Integer, Double, Character etc.
I don't think you need to know all the methods in those classes, but at the minimum do know these about wrappers:
*convert from primitive to wrapper and vice versa (eg int to Integer)
*convert from
String to wrapper and vice versa
*when using primitives as the generic type in collections (eg list, set, map), it must be the wrapper (eg no such thing as List<int> but List<Integer>)
*know the difference between parseXXX() and valueOf()
*effect of downcasting (same as primitives)
As for collection wrappers, I don't recall the objectives mention it despite the Oracle cert prep talks about it. But such collection wrappers are for special cases like synchronizing the collection. About collections in general, should know what concrete class is thread-safe or not.