Demanding book should include paintings (8)
I believe the answer is:
toilsome
'demanding' is the definition.
(thesaurus)
'book should include paintings' is the wordplay.
'book' becomes 'tome' (a tome is a book).
'should include' is an insertion indicator.
'paintings' becomes 'oils' (oil paintings).
'tome' going around 'oils' is 'TOILSOME'.
(Other definitions for toilsome that I've seen before include "Needing much effort" , "laborious" , "needing much work" .)