Well, the only tip I can think of is that the actual exam will be much easier.
60% on Devaka's exams means that you command respect from my side
I could only score 52% max :P
Concurrency questions would include, for example, the usage of start() twice (which leads to an exception), how to start threads using anonymous class arguments, etc. I didn't really get a synchronized block logic question on my exam, come to think of it, neither deadlock....but don't let your guard down. I was extremely lucky in this regard.
Generics questions will include compilation with warnings, type safety using the wildcard, generic classes and method declarations, etc.
A good garbage collection question I got said that in a class GC which owned an instance variable of itself, in one of it's methods we were creating Object instances and nullifying GC references. I had to think of it as if some imaginary reference was already referring to *this* GC instance, and that got nullified/reassigned. Just make diagrams for that and you're good to go.
All the best!