As per the usual Nolan veil of secrecy around the project, there is no word as to what character Gordon-Levitt will be playing. Although some sites are speculating that he could possible be playing Edward Nigma, aka The Riddler, there has been no confirmation that that character is going to be in the movie. The film already has some villains in Tom Hardy’s casting as Bane and Anne Hathway’s as Selina Kyle/Catwoman. Presumably, the script also has plenty of possible roles outside of Batman’s rogues gallery to play.
Gordon-Levitt is currently in production on Rian Johnson’s science-fiction thriller Looper and once he wraps on that is expected to move right over to Dark Knight Rises for its spring scheduled shooting. He is also set to reprise his role as Cobra Commander when GI Joe 2 begins filming this summer, though that project still has not hired a director.