Princeton is an Ivy League Institution with a varied Academic outreach. The list of courses taught at Princeton have been listed at: https://www.princeton.edu/academics/areas-of-study . You haven't mentioned the course you want to study in Princeton. The eligibility criteria depend on the course you want to pursue. For admission to a particular course, you can take the SAT subject test to demonstrate your knowledge and understanding of that subject. Subject tests are offered in Literature, History, Mathematics, Sciences and Foreign languages. So if you are a PCB student, you can take science subjects and appear for SAT. Though there is no specific requirement for Princeton, you will need to score more than 1440 to be even considered for Princeton.