Composer put out missing opening in capital of Italy (7)
I believe the answer is:
rossini
'composer' is the definition.
(Italian composer Gioachino Rossini)
'out missing opening in capital of italy' is the wordplay.
'out missing opening' becomes 'ross' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'capital of' suggests taking the first letters.
The initial letter of 'italy' is 'i'.
'ross'+'in'+'i'='ROSSINI'
'put' is the link.
Can you help me to learn more?
(Other definitions for rossini that I've seen before include "Staff writer" , "Composer of the opera William Tell, d. 1868" , "Barber of Seville writer" , "He composed operas" , "whose barber was in Seville" .)