Whistle-blower collaring vacuous pair's dog (8)
I believe the answer is:
springer
'dog' is the definition.
(I've seen this before)
'whistle-blower collaring vacuous pair's' is the wordplay.
'whistle blower' becomes 'singer' (I can't explain this - if you can you should believe this answer much more).
'collaring' is an insertion indicator.
'vacuous' says to hollow out the word (remove centre letters).
'pair' with its middle taken out is 'pr'.
'singer' going around 'pr' is 'SPRINGER'.
Can you help me to learn more?
(Other definitions for springer that I've seen before include "A spaniel; stone in arch" , "Large spaniel with wavy silky coat" , "hound" , "Type of spaniel" , "Game dog" .)