Joku-usin Shrine is located on the Thunderhead Isles in the Faron Grasslands Sky.
Shrine Location
Joku-usin Shrine is located at 1074, -3347, 0786 on the Thunderhead Isles in the Faron Grasslands Sky.
Proving Grounds: Short Circuit
Take the weapons from the rack near the entrance. Then make your way through the area, and defeat a Construct that has a bow. Then take the shock fruits. Attach a shock fruit to an arrow and shoot one of the metal platforms that some Constructs are standing on. This will defeat it instantly. Do the same with the other metal platform.
The remaining Constructs are on a platform that has a ring of metal plates. When the three Constructs are near each other, shoot a shock fruit at the metal floor between where all three Constructs are. The weaker Constructs will be defeated, leaving only the Captain.
After you defeat all the Constructs, the gate opens. Go through and open the chest to get an Electro Elixir. Then check on the dragon ring to get a Light of Blessing and complete the shrine.