City and I separately probing blue material (cheesy stuff) (8)
I believe the answer is:
pecorino
'separately probing blue material cheesy stuff' is the definition.
The definition suggests a singular noun which matches the answer.
'city and i' is the wordplay.
I cannot really understand how this works, but
'city' could be 'ec' (the City of London postcode) and 'ec' is located in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
'i' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for pecorino that I've seen before include "Italian sheep's cheese" , "Hard cheese!" , "Italian cheese made from ewe's milk" .)