What is singular possessive of Cris?

There are two accepted forms for possessive singular nouns that ends with an s:
Add an apostrophe (') after the existing s at the end of the Word:

• Cris'

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

• Cris's

Examples:

Cris' bicycle is new.

Cris's bicycle is new.