How do you write singular possessives?

A singular noun is a Word for one person, place, or thing (a neighbor, a town, a book).
A possessive noun is a Word that show's something in the sentence belongs to that noun.
A noun is made possessive by adding an apostrophe -s to the end of the Word (or just an apostrophe to the end of plural nouns already ending in -s). Examples of singular possessive nouns:

• a neighbor's house
• the town's mayor
• the book's cover

There are two accepted forms for possessive singular nouns that end with an s:

Add an apostrophe (') after the existing s at the end of the Word:

• boss'

Add an apostrophe s ('s) after the existing s at the end of the Word:

• boss's

Examples:

Put the mail on the boss' desk.

put the mail on the boss's desk.