Good dog's babies start to yap. Scintillating! (8)
I believe the answer is:
glittery
'scintillating' is the definition.
(I know that scintillating can be written as glittery)
'good dog's babies start to yap' is the wordplay.
'good' becomes 'g' (abbreviation).
'dog's babies' becomes 'litter' (I can't explain this - if you can you should believe this answer much more).
'start to' indicates taking the first letters.
The first letter of 'yap' is 'y'.
'g'+'litter'+'y'='GLITTERY'
Can you help me to learn more?
(Other definitions for glittery that I've seen before include "Brightly shining" , "snazzy" , "Sparkly" .)