A show dog? (7)
I believe the answer is:
pointer
'a show dog?' is the definition.
'pointer' can be an answer for 'dog?' (pointer is a kind of dog). I'm not certain of the 'a show' bit.
'show dog?' is the wordplay.
'show' becomes 'point' (synonyms).
'dog?' becomes 'er' (I can't justify this - if you can you should believe this answer much more).
'point'+'er'='POINTER'
Can you help me to learn more?
(Other definitions for pointer that I've seen before include "helpful tip!" , "Dog; cursor" , "Indicator" , "Guide" , "Game dog, used for its ability to scent" .)