ID Card #28 is a collectible item in Dead Island, and can be found in the Hotel Map of Act I. It is part of the My collectibles, let me show you them! challenge, and the Gotta find'em all and Nearly there achievements. This collectible is only accessible during the Born to be Wild quest. Once the quest is completed the elevator shaft will be closed and you will not be able to access any other Hotel area past the lobby.
Inside the hotel, in hallway right after you jump down on the elevator.
Can be seen on the following map: