He will stick at his job (10)
I believe the answer is:
billposter
'his job' is the definition.
The definition suggests a singular noun which matches the answer.
'he will stick' is the wordplay.
'he' becomes 'bill' (short for William).
'will stick' becomes 'poster' (I can't explain this - if you can you should give a lot more credence to this answer).
'bill'+'poster'='BILLPOSTER'
'at' is the link.
Can you help me to learn more?
(Other definitions for billposter that I've seen before include "One who sticks at his job" , "One pasting up advertisements" , "One who pastes up adverts on hoardings" .)