FIND the chest? WHAT

Act 1: The wrecked boat in the Kayran lair. Take the key from a corpse on one side, open the chest in another side. Go to Louis or Loredo and ask them to send some mail. They have a chest on their table, place it there. If you Jedi Mind Trick (Axii) Louis you can read his mail. If you kill Loredo, you can take his key and read his mail in addition to reveal some "secrets" about them.
Act 2: Find the wrecked ship in the SW of the map. Open the chest with the key from Act 1. Don't use any of the items till you finish this quest in Act 3, which I hadn't got to yet and craft superior armor with it.