The most common and most likely answer to this crossword clue is the 9 letter word SCOUNDREL
I've seen this crossword clue in The Guardian
S
C
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More clues leading to the result SCOUNDREL
- Sort of cruel son that pinches daughter?
- Cold nurse is horrible and not a very nice person at all!
- Suspect cold nurse is a rogue
- Cruel dons trashed patriot in last resort?
- Villain gives poor Don ulcers
- Rogue caught cracking safe’s about to face term in jail
- Lout knocked nurse cold
- Loner, “Scud”, rotten blighter
- Rogue nurse’s cold treatment not satisfactory at first
- Villain misled counsel about daughter whose body’s disappeared
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 = scoundrel.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 SCOUNDREL mean?
SCOUNDREL noun- A mean, worthless fellow; a rascal; a villain; a person without honour or virtue.