The non-attendance of Jack, the scene-shifter (7)
I believe the answer is:
absence
'the non-attendance' is the definition.
(I've seen this before)
'jack the scene-shifter' is the wordplay.
I cannot quite see how this works, but
'jack' could be 'ab' (both can mean a sailor) and 'ab' is located in the answer.
an anagram of 'scene' is 'sence' which is within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for absence that I've seen before include "Want (of something)" , "Non-attendance" , "It may make the heart grow fonder" , "Failure to show" , "form of inattention?" .)