This is hers

This is hers.

That is not a question. It is a statement.

This - a demonstrative pronoun.
is - verb
hers - a possessive pronoun, singular, feminine

The interrogative pronouns in English are these five: what, which, who, whom, and whose.

I'm sorry.I made a mistake.This is hers.I mean is "This" a demonstrative pronoun or a demonstrative adjective?

This box is hers. (This is a demonstrative adjective.)
This is hers. (This is a demonstrative pronoun.)

Here is a handy diagram.