Scan a red composition (4)
I believe the answer is:
read
'scan' is the definition.
(I know that scan can be written as read)
'a red composition' is the wordplay.
'composition' indicates an anagram (letters arranged or composed in a different order).
'a'+'red'='ared'
'ared' anagrammed gives 'READ'.
(Other definitions for read that I've seen before include "Run one's eye over" , "Lecture" , "Con" , "Absorbed (written text)" , "Interpret printed matter" .)