Here are the general rules to follow to show possession or ownership of singular and proper nouns.
To form the possessive of a singular, proper, or common noun, add an apostrophe and -s or -'s to the owner's name.
Example:
To form the possessive of proper names ending in -s or -z, add an apostrophe and -s or -'s to the owner's name.
Examples:
To form the possessive of a religious or a Greek name ending in -s or a name ending in an /-ez/ sound, add an apostrophe (').
Examples:
To form the possessive of proper names ending in -s followed by a word beginning with s, add an apostrophe (') only.
Example:
Note: It can also be with an apostrophe and an -s or -'s.
Example:
Both are correct.