Once you have saved the coward son of the blue King, you will have to collect 2 green moons to progress with the story.
Both can be found in the area with the red crystal. (If you are lost, you can get there through the area with the giant pickaxe and the underground cave that has some lava at the beginning)
One green moon can be accessed from below. You should find a hole somewhere in the middle of the stone structures. If you did not find it before, it should be covered with glass (destroyable by stomping).
Once below, activate the magnetism ability and reach the ceiling, afterwards throw the translocator in the small space inside the closed area with the chest containing the moon.
The other green moon is simply enclosed in stones, and there is a small opening for the translocator ball. You need to get in and out with the translocator both times. Contrary to the other moon, there is no lever to open a brick door from the inside.