Build on island group after influx of key capital (5,5)
I believe the answer is:
addis ababa
'capital' is the definition.
(capital of Ethiopia)
'build on island group after influx of key' is the wordplay.
'build on' becomes 'add' (I've seen this in another clue).
'island' becomes 'is' (abbreviation).
'group after influx of' becomes 'abab' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'key' becomes 'A' (musical key).
'add'+'is'+'abab'+'a'='ADDIS ABABA'
Can you help me to learn more?
(Other definitions for addis ababa that I've seen before include "place in Africa" , "Capital of Ethiopia" , "African capital" , "Unaccompanied" , "Ethiopian capital" .)