Singular: city Singular possessive: city's Plural: citiesPlural possessive: cities'
No, it's is a contraction of it is or it has. The possessive form of it is "its." Possessive pronouns don't use an apostrophe to indicate possession, the pronoun itself is the possessive form.
The possessive of it is its. Remember, if your noun ends in s, you still add 's for singular possessive.
Since "moose" is both singular and plural, "moose's" is both the singular possessive and plural possessive.