University cleaner in most superior European capital (9)
I believe the answer is:
bucharest
'european capital' is the definition.
(I've seen this before)
'university cleaner in most superior' is the wordplay.
'university' becomes 'u'.
'cleaner' becomes 'char' (charwoman is a type of cleaner).
'in' indicates putting letters inside.
'most superior' becomes 'best'.
'u'+'char'='uchar'
'uchar' inserted into 'best' is 'BUCHAREST'.
(Other definitions for bucharest that I've seen before include "Romanian capital" , "European city" , "Capital of Romania" , "Balkan city" , "European capital" .)