The most common and most likely answer to this crossword clue is the 8 letter word PAPILLON
P
A
P
I
L
L
O
N
More clues leading to the result PAPILLON
Buddy explains!

The straight part
We know that "dog" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dog = papillon.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PAPILLON mean?
PAPILLON noun- A breed of small dog with large ears; a dog of that breed.