There are two accepted forms that show possession for singular nouns ending in s:
Add an apostrophe (') after the existing s at the end of the word: James'
Add an apostrophe s ('s) after the existing s at the end of the word: James's
Examples:
We're going to James' birthday party.
We're going to James's birthday party.
James's. All possessives take " 's " except for words which end in "s" because they are plurals. James does not end in an "s" because it is a plural; it is not a word for more than one Jame.
James’
The possessive form is Amos's.
The singular possessive form is herd's.
The singular possessive form is heart's; the plural possessive form is hearts'.
The singular possessive form is grotto's.
The singular possessive form is lesson's.
The possessive form is Amos's.
The singular form is goose; the singular possessive form is goose's.The plural form is geese; the plural possessive form is geese's.
Quantum is singular, not singular possessive. The singular possessive form is quantum's.
The singular possessive form is speculum's.
The singular possessive form is frontiersman's.
The singular possessive form is aircraft's.
The singular possessive form is week's.
The singular possessive form is contralto's.
The singular possessive form is herd's.
The singular possessive form is heart's; the plural possessive form is hearts'.
The singular form for the noun families is family. The singular possessive form is family's.
The singular possessive form of wolves is wolf's.