Top dog, from what we hear (4)
I believe the answer is:
peak
'top' is the definition.
('peak' can be a synonym of 'top')
'dog from what we hear' is the wordplay.
'dog' becomes 'peke' (Peke is an example).
'from what we hear' shows a homophone (sound like).
'peke' sounds like 'PEAK'.
(Other definitions for peak that I've seen before include "Summit, often pointed" , "'Heyday'" , "Sharp pointed summit" , "High point" , "maximum pitch" .)