Spotted going back about key requirements (5)
I believe the answer is:
needs
'spotted going back about key requirements' is the definition.
'needs' can be an answer for 'requirements' ('need' can be a synonym of 'requirement'). I'm unsure of the 'spotted going back about key' bit.
'going back about key requirements' is the wordplay.
'going back' is a reversal indicator.
'about' indicates putting letters inside.
'key' becomes 'd' (musical key).
'requirements' becomes 'seen' (I can't justify this - if you can you should believe this answer much more).
'd' put into 'seen' is 'sdeen'.
'sdeen' reversed gives 'NEEDS'.
Can you help me to learn more?
(Other definitions for needs that I've seen before include "Necessitates" , "Necessities" , "Requires, is in want of" , "Can't do without" , "Calls for" .)
