After that take this printout to any registered Doctor (A Legal Physician) and that doctor will do the necessary….

Hello friend, just take the printout of page 53(Annexure 8) from business rules pdf from josaa website. You see at the last of the medical certificate there's registration number that's the registration number(Every Legally Medicine Practicing Doctor has this number) of the doctor that will do Your checkup for this certificate. And the seal has to be of the hospital where he/she works. That seal must be of any government hospital.

All the best!!!