What would be the possesive form of a noun?

Answer 1

A "regular" noun has four forms: two standard (singular and plural) and two possessive (also singular and plural). Here are some examples:

girl, girls (standard)
girl's, girls' (possessive)

house, houses
house's, houses'

family, families
family's, families'

child, children
child's, children's

man, men
man's, men's

... and lots of others. Do you have any specific nouns in mind?