Former pupil, able to read note, is destroyed (11)
I believe the answer is:
obliterated
'is destroyed' is the definition.
(similar in meaning)
'former pupil able to read note' is the wordplay.
'former pupil' becomes 'OB' (abbreviation for 'Old Boy' - private school pupil).
'able to read' becomes 'literate' (I've seen this before).
'note' becomes 'D' (musical note).
'ob'+'literate'+'d'='OBLITERATED'
(Other definitions for obliterated that I've seen before include "completely removed" , "trashed" , "made hard to read" , "Effaced" , "Erased" .)