Where there's no longer a gnarled tree (6)
I believe the answer is:
exeter
'where' is the definition.
The definition suggests a singular noun which matches the answer.
'there's no longer a gnarled tree' is the wordplay.
'there's' says to put letters next to each other.
'no longer' becomes 'ex' (prefix meaning former or onetime).
'a gnarled' indicates an anagram (gnarled can mean twisted).
'tree' is an anagram of 'eter'.
'ex' next to 'eter' is 'EXETER'.
Can you help me to learn more?
(Other definitions for exeter that I've seen before include "City in 5 Down" , "South-west English city" , "The modern Isca Dumnoniorum" , "Devonshire city" , "Devon university city" .)