Hello,

Registration number is the student's enrollment number/application number which you would have got at the time of form submission or registration(for class 10) during class 9. Usually it's easy to get the registration number through admit card or marksheet of student. But this year since the scenario is different due to pandemic situations, you can try contacting your school and take help from there or you can wait till your class 10 results are announced.

Hope this helps.

Good luck!!!