For example, are you asking about:
* A specific breed of dog? There are many breeds that start with the letter "G", like Golden Retriever, German Shepherd, Great Dane, etc.
* A nickname for a dog? Maybe you're thinking of a specific dog you know, and "G dog" is a nickname they have.
* A slang term? "G dog" might be a slang term in a specific community.
Please give me more information so I can help you figure out what kind of "G dog" you're looking for!