In our September issue, we asked you how you format the possessive form of a proper noun ending in s (e.g., the Jones dog).
I add an apostrophe only (e.g., the Jones’ dog). 70% (235 votes)
I add an apostrophe and an s (e.g., the Jones’s dog). 27% (92 votes)
I add neither an apostrophe nor an s (e.g., the Jones dog). 1% (5 votes)
I use another format. 1% (5 votes)
What You Said
Actually, assuming the Joneses are a family, I would probably make it “the Joneses’ dog.” My name is Jones, so I know these things.