I'm no CX expert, but have seen on PPrune and other places that CX will base you wherever, but you have to have the legal right to work in "wherever", i.e., you have to be a citizen. They have bases in Paris, London, Frankfurt, etc., for nationals from those places. The only exception is Hong Kong - I think anybody can be based out of there, that's why they go through the process to get you the HK flying tickets during training. So, for your average American, my understanding is you will work out of US bases and/or HK (unless you have the legal right to work out of some other country).