How much information do the alumni interviewers know about the applicant beforehand? Only personal info like name age gender etc, or the whole application including essays and extracurriculars?
They know your name, age, gender, school in which you are applying to, and school in which you are applying from. They also have your email and phone number. But no, they definitely do not see (nor do they likely have the time to) your essays or ECs.
They do not see your gpa or test scores either
We have very basic information: name, contact details, gender, high school, school you are applying to, and major you indicated (if you selected one). We don’t have scores, grades, ECs, or current schedules. We don’t need that information although during the interview a student might be asked about the classes they are taking or what ECs and activities they enjoy. I almost always open a conversation with asking about how senior year is going which usually ends up with a discussion of current classes.
I’m not interested in grades or scores - that’s already part of the application. I don’t have time to read essays and I don’t have access to them anyway (although a student once tried to give me essays; I declined). I’m interested in having a conversation and in finding out what the student is like, what they like to do, and how I feel they’d do at Penn.