For this artwork, one needed to concentrate a long time? (5,4)
I believe the answer is:
still life
'for this artwork' is the definition.
(type of painting or drawing)
'one needed to concentrate a long time?' is the wordplay.
'one needed to concentrate' becomes 'still' (device used to distil or concentrate drinks).
'a long time?' becomes 'life' (the longest prison sentence).
'still'+'life'='STILL-LIFE'
(Other definitions for still life that I've seen before include "Composition" , "Painting genre" , "rt-form" , "Drawing" , "artwork" .)