Graduate in capital with citadel (6)
I believe the answer is:
casbah
'citadel' is the definition.
(I've seen this before)
'graduate in capital' is the wordplay.
'graduate' becomes 'ba'.
'in' means one lot of letters goes inside another.
'capital' becomes 'cash' (I can't justify this - if you can you should believe this answer much more).
'ba' going inside 'cash' is 'CASBAH'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for casbah that I've seen before include "North African citadel" , "Crowded part of old Arab city in N Africa" , "Arab quarter" , "Citadel of N African cities" , "area round Algiers fortress" .)