Knack to be busy with illustrations, etc. (7)
I believe the answer is:
artwork
'busy with illustrations etc' is the definition.
I can't judge whether this definition defines the answer.
'knack to be' is the wordplay.
'knack' becomes 'art' (both can mean a skill or talent).
'to be' becomes 'work' (synonyms).
'art'+'work'='ARTWORK'
Can you help me to learn more?
(Other definitions for artwork that I've seen before include "Illustrations and designs for printing" , "Painting" , "Illustrations in book" , "Graphics" , "Illustrative material in publication" .)