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.
No, the word "it" is a singular pronoun, a word that takes the place of a noun for one thing.The word "it" is not a possessive form.The possessive pronoun and possessive adjective is its.
The possessive word for Priscilla is "Priscilla's."
The possessive form of the word dictionary is dictionary's.
Two possessive forms of the word you are your and yours.
Taco's is the singular possessive.
The singular possessive form is word's, for example the word's definition.
The possessive word for son is "son's."
Julia's (possessive)
possessive form of the word glass: glass'
The possessive form of the word "month" is "month's."
possessive form of the word Congress: Congress'
possessive plural word for the bishops: bishops'