Declares the donkey needs to rest anew (7)
I believe the answer is:
asserts
'declares' is the definition.
(asserting is a kind of declaring)
'donkey needs to rest anew' is the wordplay.
I cannot quite see how this works, but
'donkey' could be 'ass' (ass is a term for a donkey) and 'ass' is found in the answer.
an anagram of 'rest' is 'erts' which is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'the' acts as a link.
Can you help me to learn more?
(Other definitions for asserts that I've seen before include "States categorically" , "Declares to be true" , "States firmly" , "States confidently and forcefully" .)