Chapter 4-1: The Sacred Pool
Amulet Piece #11: Once you receive the water power, make your way to the first large drop and then you will come to this room. When you do, look for the opening in the ceiling then draw a spout to take you into it and find the piece.
Chapter 4-2: The Great Fall
Amulet Piece #12:
When you reach the part where you need to knock over the large log blocking the path, do so and then ride down it to the right side. Up above is where the piece is, so you will need to hop up onto the log then draw out the branch on the right, before jumping up again to the ledge above to reach it.