Dead Island Side Quests Walkthrough: My Precious
You get this sidequest from Jeannine in the lifeguard tower. She says she left her necklace in her room and asks you to go retrieve it. The necklace can be found in Bungalow 6 in the Silver Bungalows district.
It is advised you take the truck to get there (assuming you have finished the Lazarus Rising sidequest)
Follow the radar and head over to the Silver Bungalows area.
Once you reach the Bungalow, you will notice another truck blocking the entrance. Back it up, so that you can access the room.
Search the room for the necklace. It should be on one of the shelves.
Also, while here, pick up the Bloody Valentine Quest from the bleeding guy in the bathroom.
Bring the necklace back to Jeannine in the lifeguard station to complete the quest.