A national topic of discussion (7)
I believe the answer is:
subject
This clue might be a double definition.
'a national' is the first definition.
(I know that national can be written as subject)
'topic of discussion' is the second definition.
'subject' can be an answer for 'topic' (synonyms). I am not certain of the 'of discussion' bit.
Can you help me to learn more?
(Other definitions for subject that I've seen before include "Topic - branch of study - citizen" , "Expose; field of study" , "Theme (of a fugue)" , "Topic being discussed" , "guinea pig" .)