Q. When a person's name ends in "s," how do you form the possessive?

If a person's name ends with an "s", such as James, you are wanting to show a singular noun (James) that ends in an "s" as being possessive. How you form the possessive depends on which style guide your subject area or your assignment is using. 

For American Psychological Association (APA), which is commonly used in the social and behavioral science as well as nursing, business and other natural sciences the position of the apostrophe depends on the whether you are referring to a singular or plural noun. 

• A singular noun that ends with s, you will add a 's. Example: James's

For more information go to the link on APA's use of possessive nouns. 

Luckily, Chicago Manual of Style (CMOS), commonly used in the humanities as well as art and literature and Modern Language Association (MLA), and Modern Language Association (MLA) style, used in English, literature, philosophy and languages, follow a similar convention as APA. 

For more information on use of singular possessive nouns in APA, CMOS and MLA click on this link from OWL Purdue. 

If you are not using, APA, CMOS, and MLA please check the style guide of whatever format you're using to make sure you're in line with their recommendations.