Are the sentence where were you are pronoun predicate nominative?

No, in the sentence, "Where were you?", the pronoun "you" is not a predicate nominative.

A predicate nominative (also called a subject complement) is the noun or a pronoun following a linking verbthat restates or stands for the subject.

The verb "were" in this sentence is not a linking verb. The pronoun "you" does not restate the Word "where".

An example of the pronoun "you" as a predicate nominative:

"The winner is you." (winner = you).

An example of the verb "were" as a linking verb:

"Those birds were pigeons." (birds = pigeons)