What is the noun and possessive noun of class?

The noun "class" is a singular, common noun.

The noun "class" is a concrete noun as a Word for a group of people.

The noun "class" is an abstract noun as a Word for a category of people or things having some property or attribute in common.

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: class'

Add an apostrophe s ('s) after the existing s at the end of the Word: class's

Examples:

The class' trip is scheduled for Thursday.

The class's trip is scheduled for Thursday.