If I wanted to say--This is Jos's backpack. Would the comma go between the s's as I have included, or would there just be a comma after the s?
What is the person's name? Jos?
And I think you mean apostrophe, right? Not comma?
It's an apostrophe, not a comma.
If the boy's name is Jos -- then it would be Jos's backpack.
If the name is Joss, then you'd write it this way: Joss' backpack.
To correctly indicate possession in this case, you should use an apostrophe after the second "s" in "Jos's." This is called the "double possessive" or "postpositive genitive." However, the placement of the comma depends on whether you are using American or British English.
In American English, placing a comma between the two "s's" is optional but not commonly used. Therefore, the correct form would be "Jos's backpack."
In British English, a comma is usually added before the possessive "s." So, the correct British English form would be "Jos's, backpack."
That being said, it's important to note that the specific usage and style guide you are following may have different guidelines. It's always a good idea to consult the appropriate style guide or reference material to confirm the preferred punctuation in your specific context.