Where a girl turns up after six (6)
I believe the answer is:
vienna
'where a' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'girl turns up after six' is the wordplay.
'girl' becomes 'anne' (girl's name).
'turns up' is a reversal indicator.
'after' means one lot of letters go next to another.
'six' becomes 'VI' (Roman numerals).
'anne' written backwards gives 'enna'.
'enna' put after 'vi' is 'VIENNA'.
Can you help me to learn more?
(Other definitions for vienna that I've seen before include "Adult home of Beethoven, Brahms, Mozart and Schubert" , "Austria's capital city" , "Strauss 'Tales from the . . . . . . Woods'" , "Austrian city of the waltz" , "huge 20 [ULTRAVOX] hit" .)