After watching the trailer multiple times it seems pretty clear to me that Gordon knows Bruce Wayne is Batman.
First of all Gordon is talking to Wayne based on the fact that Bale is speaking like Bruce Wayne and not Batman.
If you listen closely Gordon is telling Wayne "We were in this together"...."then YOU were gone"
He goes on to say "The Batman must come back"
which Bruce(obviously speaking normal) replies "What if he doesn't exist anymore?"
If he was indeed Batman while visiting Gordon I highly doubt Gordon would be saying the Batman must come back. Given the fact that if Wayne was dressed as Batman he would already be back.
I believe Gordon know's Wayne is Batman and he is asking him to wear the mask once again. (presumably because he is still in hiding from the events in The Dark Knight)
Thoughts?