Listen twice to exclamation of approval (4,4)
I believe the answer is:
hear hear
'exclamation of approval' is the definition.
(I've seen this before)
'listen twice' is the wordplay.
'listen' becomes 'hear' (I've seen this in another clue).
'twice' says to double the letters.
'hear' doubled is 'HEAR HEAR'.
'to' acts as a link.
(Other definitions for hear hear that I've seen before include "express approval" , "I strongly approve" , "Listen, listen - it's an endorsement" , "That's right" , "expressed approval" .)