Is the possessive form of witness witness'?

Answer 1

There are two accepted forms for possessive singular nouns ending in s:

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

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

Examples:

The witness' statement was added to the police report.

The witness's statement was added to the police report.

Note: If you are a student, use the form that is preferred by your teacher.