Engineer answers a riddle at last, demonstrating knowledge (9)
I believe the answer is:
awareness
'knowledge' is the definition.
(awareness is a kind of knowledge)
'engineer answers a riddle at last' is the wordplay.
'engineer' is an anagram indicator.
'at last' says to take the final letters.
The last letter of 'riddle' is 'e'.
'answers'+'a'+'e'='answersae'
'answersae' is an anagram of 'AWARENESS'.
'demonstrating' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for awareness that I've seen before include "Fact of consciousness" , "Knowledge (of a fact)" , "Knowing" , "understanding" , "Consciousness, sentience" .)