It's very wearing, you say emphatically (6)
I believe the answer is:
stress
'say emphatically' is the definition.
'stress' can be an answer for 'say' (stressing is a kind of saying). I'm unsure of the 'emphatically' bit.
'it's very wearing you' is the wordplay.
'it's very' becomes 'tres' (French).
'wearing' is an insertion indicator.
'you' becomes 'ss' (I can't justify this - if you can you should believe this answer much more).
'tres' inserted into 'ss' is 'STRESS'.
Can you help me to learn more?
(Other definitions for stress that I've seen before include "Lay emphasis on - it's a strain" , "Dwell on" , "Emphasise the pressure" , "Emphasis on anxiety?" , "Emphasis: result often of being under pressure" .)