Add ’s to create the possessive, even for singular names ending in an s, x, z

Jones’s art, Xerox’s bill, Bill Buzz’s restaurant

If the name is plural, add the apostrophe after the s.

the Joneses’ art

With a compound subject, put the apostrophe after the second name:

Doug and Linda’s house

If the subject is not compound but two separate entities, both take an apostrophe:

students’ and faculty’s health plans

Exceptions: Nouns that are the same in both singular and plural form: politics’; species’

Some “for sake” expressions: for goodness’ sake; but for appearance’s sake.