The singular possessive is hostess's.

The plural possessive is hostesses'.

Hostess is a noun.

The correct singular possessive form for the noun hostess is hostess's.

A hostess is a female host. A host and hostess are the people who invite others to their home or place of business. If you throw the party at your house, you are the host or if you are female, the hostess. If the meeting is held in your building, you are the host or hostess.

A hostess is female; a host is the male.