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:
Add an apostrophe s ('s) after the existing s at the end of the word:
. Examples:
"The farmer pulled out the ass' feed and put it in the tray".
"The farmer pulled out the ass's feed and put it in the tray".
Quantum is singular, not singular possessive. The singular possessive form is quantum's.
The singular possessive form of "test" is "test's".
The singular possessive pronouns are "my," "mine," "your," "yours," "his," "her," and "its."
The singular possessive of "ant" is "ant's" and the plural possessive is "ants'".
Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.
The singular possessive form of "classmate" is "classmate's."
The singular possessive of dish is dish's
Taco's is the singular possessive.
Grave's is the singular possessive.
The singular possessive is Martin's.
The singular possessive is fish's.
Buzz's is the singular possessive.