Question about rucksack's content (3)
I believe the answer is:
ask
'question' is the definition.
(thesaurus)
'about rucksack's content' is the wordplay.
'about' shows that the letters should be reversed in order.
'content' says the answer is hidden in the clue (I've seen 'contents of' mean this).
'ksa' can be found hidden inside 'rucksack'.
'ksa' back-to-front is 'ASK'.
(Other definitions for ask that I've seen before include "Enquire" , "Invite (to a party)" , "Issue invitations" , "Put a question" , "Seek an answer" .)