Since you already know the ropes, there are no military-related questions I can think of that you would not know. My personal recommendation is to tell them your story on why you want to be CEC reserves officer, why you think this is the right time for you to join, and what values you bring to the navy (i.e why should they hire you).
I personally think that they are not interested in cookie-cutter answers (being this all-American hero type answers) so be yourself and use your military and civilian experiences to your advantage.
@NuocH2O already gave out most of the questions /conversation topics. The officers who interviewed were really great folks with so much experience and humility, so it was a very relaxed setting but I did my best to maintain my military bearings (yes sir, no sir, wait till they finish talking, etc). I come from a tech-heavy background so not many questions there, but make sure you can say a list of leadership/personnel or project management type roles (both mil and civ). My only thing was after the interview, I realized that there were so many other leadership roles that I have done and should have mentioned. I mean I did prepare for it, but while describing them I did miss a few of those important ones.