Which is not a pronoun 'he' 'they' 'off' or 'you'?

The Word off is not a pronoun.

The Word off is a preposition, an adverb, and an adjective.

Examples:

We found a place to set up camp off the trail. (preposition)

Our team ran off with the trophy. (adverb)

I made cookies on the off chance that you would bring the children. (adjective)

A pronoun is a Word that takes the place of a noun in a sentence.

The pronouns he, they, and you are personal pronouns. A personal pronoun is a Word that takes the place of a noun for a specific person or thing.