Extremely abstruse answers developed knowledge (9)
I believe the answer is:
awareness
'knowledge' is the definition.
(awareness is a kind of knowledge)
'extremely abstruse answers developed' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'developed' is an anagram indicator.
'abstruse' with its centre taken out is 'ae'.
'ae'+'answers'='aeanswers'
'aeanswers' anagrammed gives 'AWARENESS'.
(Other definitions for awareness that I've seen before include "Knowing" , "State of being conscious" , "Mindfulness, consciousness" , "Consciousness,knowingness" , "Fact of consciousness" .)