It may be difficult to make out Schubert's original slow movement (6)
I believe the answer is:
scrawl
'it may be difficult to make out' is the definition.
The definition suggests a singular noun which matches the answer.
'schubert's original slow movement' is the wordplay.
'original' says to take the initial letters.
'slow movement' becomes 'crawl' (I've seen this before).
The first letter of 'schubert' is 's'.
's'+'crawl'='SCRAWL'
Can you help me to learn more?
(Other definitions for scrawl that I've seen before include "Scribbled writing" , "Poor handwriting" , "Messy drawing, possibly" , "Hasty writing" , "careless writing" .)