The exam centers of class 12th AISSCE exams are announced by the CBSE board itself. They are generally announced 2-3weeks prior to exams when you receive your admit card from the school. You'll get to know your exam center.

If you have opt for physical education in class 12th, then you don't have too appear for computer science exam. You'll have your subjects mentioned in your admit card itself, you will have to appear only for those subjects.

To pursue engineering in computer science you're supposed to have Physics, Chemistry and Math as your main subjects along with a language. Rest of the subjects don't matter much.