A rabbit hole is pointless for a donkey! (5)
I believe the answer is:
burro
'for a donkey' is the definition.
(term for a small donkey)
'a rabbit hole is pointless' is the wordplay.
I cannot really see how this works, but
'hole' could be 'o' and 'o' is present in the answer.
The remaining letters 'burr' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for burro that I've seen before include "Spanish donkey" , "Small donkey (US)" , "Small donkey used as a pack animal" , "Beast of burden" .)