What are the pronouns in an apple a day keeps the doctor away?

There is no pronoun in the saying "An Apple a day keeps the doctor away."

A pronoun is a Word that takes the place of a noun in a sentence, for example:

"It keeps the doctor away." (the pronoun 'it' takes the place of the noun phrase 'an Apple a day', which is the subject of the sentence)

"An Apple a day keeps him away." (the pronoun 'him' takes the place of the noun 'doctor')