Surveys a costumed trio passes on (7)
I believe the answer is:
studies
'surveys' is the definition.
('study' can be a synonym of 'survey')
'a costumed trio passes on' is the wordplay.
'a costumed trio' becomes 'stu' (I am not sure about this - if you are sure you should believe this answer much more).
'passes on' becomes 'dies' (passes away).
'stu'+'dies'='STUDIES'
Can you help me to learn more?
(Other definitions for studies that I've seen before include "academic courses" , "Work done to acquire learning" , "Applies the mind to learning" , "lessons" , "Scrutinises" .)