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.
The plural possessive form of "witness" is "witnesses'".
The possessive singular form of "witness" is "witness's."
The plural possessive form of "witness" would be "witnesses'."
The singular form for the plural noun witnesses is witness; the singular possessive is witness'.Example: The witness' bag was snatched as she walked away.
The plural form of the noun witness is witnesses.The plural possessive form is witnesses'.example: All of the witnesses' statements were added to the police report.
The possessive witness's pertains to something associated with a singular witness. The possessive witnesses' pertains to association with more than one individual witness (witnesses). (The exception here is for the plural ending in 's', which allows omission of the additional possessive 's', for written clarity and ease of pronunciation. Note that the singular possessive is pronounced identically to the plural AND plural possessive.)
As written in the question, 'wittiness' is an abstract noun to the state of being witty, and thus does not have a possessive form. If the writer meant 'witness', the possessive may be written as witness's or witness', both are accepted forms.
The possessive form of the singular noun judge is judge's.Example: The witness had the judge's complete attention.
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:witness'Add an apostrophe s ('s) after the existing s at the end of the word: witness'sExamples: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.Because you will add an S sound to form the possessive, most style guides recommend the apostrophe S rather than the apostrophe alone, especially for common nouns.
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:witness'Add an apostrophe s ('s) after the existing s at the end of the word: witness'sExamples:The witness' testimony seemed plausible.The witness's testimony seemed plausible.
The plural form of the noun judge is judges.The plural possessive form is judges'.Example: All of the judges' attention was focused on the witness.
Unlike "witness's", the spoken usage of "witnesses" does not normally include an extra (third) sibilant, and may be written "witnesses' ." The "s" after the apostrophe has, however, been noted regarding possessives of "Jehovah's Witnesses".