What is the pronoun to be?

The pronoun "to be" doesn't exist. "To be" is an infinitive verb phrase, not a pronoun.

Pronouns are words that replace nouns, like:

* I, you, he, she, it, we, they

* me, you, him, her, it, us, them

* mine, yours, his, hers, its, ours, theirs

Let me know if you have any other questions!