Spooner's other half meeting old king in confined space (9)
I believe the answer is:
'confined space' is the definition.
I don't understand the rest of the clue.
(Other definitions for cubbyhole that I've seen before include "Small enclosed space or room", "Snug enclosed space", "Recess to contain miscellaneous objects", "Small compartment, room space", "Place for keeping bits and bobs".)