What action does caliban suggest when e discusses killing próspero with stephano and trinculo

APEX: Burning Prosperos books

Caliban believes Prospero to be a tyrant who usurped the island from him by sorcery, and he enlists Stephano and Trinculo in order to free himself. He tells Stephano that he will lead him to where Prospero lies in order to kill him in his sleep.

To quote the relevant lines:

"Yea, yea, my lord: I'll yield him thee asleep,

Where thou mayst knock a nail into his head."