How to use the Spectre Specs

Find the Defence Against the Dark Arts class room (follow the ghost chips from the Gryffindor common room). Put the cauldron together and brew the strength potion. Once you drink it you'll be able to open cupboard on the right which triggers an event that will unlock a wider range of spells.

To the left of the wall there is a student with a ladle looking object above his head.

Go down the stairs and look for a student carrying the ladle. Zap him 3-4 times with your attack spell and he will drop it. Bring the item back to the first student and the wall will explode.