Hello aspirant,

Students have only rollno. On their marksheets, you may need regostration no. In some applicatiom so you may directly go to this official link and get the registration number after entering details:

https://www.google.com/url?sa=t&source=web&rct=j&url=http://cbseaff.nic.in/cbse_aff/School/FindRegno.aspx&ved=2ahUKEwjOwcaCosviAhUeTI8KHTQZCGgQFjAJegQIARAB&usg=AOvVaw22gqwlj0fDj5mVpMLrH011

Best of luck!!