It's the Sesame key. Use Edna card to go to Edna and give her the ribbon If you haven't the ribbon, you can get in one of the rewards after you do the JAG, if you haven't get before you must do the JAG again
Thx but that Edna makes another problem :D ... Where can I get that edna´s card ? ... I´ve been doing well until this point And I think that i´m almost at the end of the game