Work that turns up when nothing's about (4)
I believe the answer is:
opus
'work' is the definition.
(an opus is an artistic work)
'turns up when nothing's about' is the wordplay.
'turns up' says the letters should be written backwards.
'when' becomes 'up' (I am not sure about this - if you are sure you should believe this answer much more).
'nothing's' becomes 'o's' (looks like zero - 0).
'about' is an insertion indicator.
'up' in reverse letter order is 'pu'.
'pu' inserted within 'os' is 'OPUS'.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for opus that I've seen before include "Creative work, eg in writing, art or music" , "Work (mus.)" , "Work or composition, usually musical" , "Artistic work" , "Soup (anag.)" .)