What's the use of working? (10)
I believe the answer is:
employment
This clue is a double definition.
'what's the use' is the first definition.
('employment' can be a synonym of 'use')
'working?' is the second definition.
(thesaurus)
'of' is the link.
(Other definitions for employment that I've seen before include "A person's work or profession" , "The utilisation of something" , "Paid work" , "Utilization" .)