It's prominent at the quayside in Devon (3)
I believe the answer is:
tor
'quayside in devon' is the definition.
The definition suggests a singular noun which matches the answer.
'it's prominent at the' is the wordplay.
'it's prominent' becomes 'or' (I can't explain this - if you can you should give a lot more credence to this answer).
'at' says to put letters next to each other (I've seen this in other clues).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'or' after 't' is 'TOR'.
Can you help me to learn more?
(Other definitions for tor that I've seen before include "Pillar of rock" , "feature of Glastonbury" , "fell" , "eminence" , "It rises" .)