If you highlight a function name in the Primary Editor, then select "Callers" in the Assistant Editors, you can view where the highlighted function is called.
There are left and right arrows at the top of the Assistant Editor that allow you to jump to the previous/next place where the function is called. Is there a keyboard shortcut for these?
I think you need the shortcut are:
control+option+command+j is "Jump to Definition in Assistant Editor"
control+command+left/right is "Go back/forward"
And you can see and set all the shortcut on Xcode->Preference->Key Bindings