There was a question on the Clojure Google group about structural sharing in rrb-vectors visavi a zipper-construction.
As we all know, it's not very easy to be certain of how much memory is allocated in Java/Clojure since the pointers are sometimes reused, and the situation gets even more complicated (for the better) when we have structural sharing and immutable objects.
The Clojure data structures are constructed from Object arrays, which creates shallow nested trees of either vector elements or key-value pairs in the case of PersistentMaps. Likely one could use reflection to dig deeper into the the inner parts of these data structures and arrays, Iroh and Clj-wallhack seems both worthy to try out.
I created a small function for getting a pointer to every Clojure data structure from a nested structure (without taking care of it's aforementioned internals, though).
I think the best way would be to count objects with VisualVM or some other profiler, though.