Paying attention after key is sparkling (10)
I believe the answer is:
glistening
'is sparkling' is the definition.
(thesaurus)
'paying attention after key' is the wordplay.
I cannot really see how this works, but
'key' could be 'g' (musical key) and 'g' is found within the answer.
'paying attention' could be 'listening' (I've seen this in another clue) and 'listening' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for glistening that I've seen before include "flashy" , "having a sparkle" .)