Discover a spot framing church by river (9)
I believe the answer is:
ascertain
'discover' is the definition.
(ascertaining is a kind of discovering)
'a spot framing church by river' is the wordplay.
'spot' becomes 'stain' ('stain' can be a synonym of 'spot'**).
'framing' is an insertion indicator.
'church' becomes 'ce' (abbreviation for Church of England).
'by' means one lot of letters go next to another.
'river' becomes 'r'.
'ce'+'r'='cer'
'stain' going around 'cer' is 'scertain'.
'a'+'scertain'='ASCERTAIN'
(Other definitions for ascertain that I've seen before include "Get to know" , "Find out by making enquiries in sectarian way" , "Discover" , "Cartesian (anag)" , "Find out - make sure" .)