One sitting in judgement shows awareness (9)
I believe the answer is:
sentience
'awareness' is the definition.
('sentience' can be a synonym of 'awareness')
'one sitting in judgement' is the wordplay.
'one' becomes 'i' (Roman numeral).
'sitting in' is an insertion indicator.
'judgement' becomes 'sentence' (sentence is a kind of judgement).
'i' going into 'sentence' is 'SENTIENCE'.
'shows' is the link.
(Other definitions for sentience that I've seen before include "Feeling" , "awareness" , "mind" , "Consciousness -- ten nieces (anag)" , "Ability to feel or perceive" .)