Is that a conjunction

Answer 1

No. The word that is a pronoun, or an adjective.

If I say "I enjoyed that" the pronoun that stands for the thing I enjoyed (a dinner, let us say).

As an adjective, 'that' is the distant form of the adjective 'this.'

Answer 2

Yes, "is" is a form of the verb "to be." It is not a conjunction, which are words like "and," "but," or "or" that connect clauses or sentences together.