I have used all of my production Nintex workflow allocation. Is there an easy way to see exactly which of my sites/lists/libraries are using Production licences?
Not yet unfortunately. If you have Nintex Enterprise subscription and are using Nintex Hawkeye, soon you will be given "Inventory Lenses" (Advance Preview: Nintex Hawkeye Inventory LensLens) that will bring you the answers exactly to that sort of questions.
Retrieving data ...