Quest : Goblin Treasure - Collect the Treasure Keeper's Jewel and open the Goblin Treasure Chest.
Zone: Sandeep - Begonia Hilltop. http://prntscr.com/dkacx6

As seen in the screenshot there is no chest to open. After 20 minutes of waiting for it to appear and watching multiple players try to do this quest i am sure that it's currently bugged.