It’s in need of a sharpener, silly! (9)
I believe the answer is:
pointless
'silly' is the definition.
(thesaurus)
'it's in need of a sharpener' is the wordplay.
I cannot quite see how this works, but
'it's' could be 'es' ('e' can mean 'electronic' which is similar to 'IT') and 'es' is found in the answer.
'in' is present in the answer.
'of' could be 'o' and 'o' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for pointless that I've seen before include "Futile, irrelevant" , "no avail" , "Quite vain" , "Ineffectual" , "Futile - TV quiz show" .)