It shows who's to work or rest, maybe (6)
I believe the answer is:
roster
'it shows who's' is the definition.
The definition suggests a singular noun which matches the answer.
'work or rest maybe' is the wordplay.
'work' indicates anagramming the letters.
'maybe' indicates anagramming the letters.
'or' with letters rearranged gives 'ro'.
'rest' anagrammed gives 'ster'.
'ro'+'ster'='ROSTER'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for roster that I've seen before include "Schedule" , "Duty plan" , "Duty list for sorter" , "List showing turns of duty" , "Resort (anag)" .)