After you get Misko's treasures from Cephla Lake Cave, you can pay Domidak and Prissen to learn about the twins treasure.

Quest Location

If you have completed Misko's Cave of Chests and Misko's Treasure: The Fierce Deity, you can talk to Domidak and Prissen outside of Cephla Lake Cave and pay 100 rupees to learn about the twins treasure.

How to Complete the Quest

Go into Dueling Peaks North Cave to find the "little twin's sign" that the manuscript refers to. Then go into Dueling Peaks South Cave and place rocks on the correct buttons, as indicated in the pattern on the ceiling in Dueling Peaks North Cave (see above). The door in the cave will open and you can open the chest to get Tingle's Shirt.