Not to be a smartass but just ask the questions you would like answers to. You need to make sure this job is a good fit for you in case you get an offer. You probably have an idea of what aspects of RP you enjoy most ( job coverage, lead tech, alara, instrumentation, etc) so you may want to ask how the natural progression goes at that plant.
Dont ask about salary or relocation and definitely don't ask how soon you can transfer out of the department!