Subject of examination (6)
I believe the answer is:
testee
'subject of examination' is the definition.
(someone being tested)
'subject of examination' is the wordplay.
I cannot quite see how this works, but
'subject' could be 'ee' (EE is an example) and 'ee' is located in the answer.
'examination' could be 'test' (synonyms) and 'test' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for testee that I've seen before include "exam candidate" , "Someone taking exam" .)