Set up second form for, say, reading breaks on vessel (6)
I believe the answer is:
rework
'set up second form for say' is the definition.
I can't judge whether this definition defines the answer.
'reading breaks on vessel' is the wordplay.
'reading' becomes 'r' (one of the traditional three R's of education).
'breaks' means one lot of letters goes inside another.
'on' becomes 're' ('on' can be mean 'with reference to').
'vessel' becomes 'wok' (I am not sure about this - if you are sure you should believe this answer much more).
're'+'wok'='rewok'
'r' inserted into 'rewok' is 'REWORK'.
Can you help me to learn more?
(Other definitions for rework that I've seen before include "Fashion again" , "What editors do" , "Alter, revise" .)