you will get an email stating what state you were selected for. it will also say if it will be terminal or enroute. depending on the state you can sometimes figure it out, for instance, utah, and denver (for example) only have one enroute facility, so if you got an email saying you were selected for the enroute option for one of these states (or any other state with one type of facility, whether it is terminal or enroute) then it is pretty easy to figure out where you are going. Past that, its tough to tell unless you know somebody 'on the inside'. does this make sense?
also, its good to remember that SOMETIMES things change, so until you get it IN WRITING on a FOL the facility could change. once you get to your pepc you will get it in writing (TOL) where you are going to go, and there is a good chance that it will be the facility you are going to (well say 99% chance).
hope you understood all that, if you have any questions feel free to PM me