ID Card #46 is a collectible item in Dead Island, and can be found in the Resort 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.
It's on a desk in the pump control room, where you cut the water flow for the Let the Waters Flow quest. During your first visit to the Sewers.
Can be seen on the following map:
ID Card 46, Location (not available)