Chapter not so much about French writer’s skill (10)
I believe the answer is:
cleverness
'skill' is the definition.
(I've seen this in another clue)
'chapter not so much about french writer's' is the wordplay.
'chapter' becomes 'c' (abbreviation).
'not so much' becomes 'less' (I've seen this before).
'about' indicates putting letters inside.
'french writer' becomes 'verne' (author Jules Verne).
'less' enclosing 'verne' is 'leverness'.
'c'+'leverness'='CLEVERNESS'
(Other definitions for cleverness that I've seen before include "Quick intelligence" , "Skill, adroitness" , "genius, perhaps" .)