Hello

AIIMS MBBS 2019 application process is divided into two steps- Basic Registration and Final Registration. 
During the basic registration process of AIIMS application form, aspirants need to fill their personal details, contact details and upload the scanned images of passport size photograph, signature and left-hand thumb impression. While, in the final registration, the remaining details such as qualification details, payment, city choice and printout of the registration form will be done.

Are you asking the requirement of OBC NCL certificate during the basic registration? OBC NCL Certificate is not required during the registration. You just need to upload Photograph, Signature and Left thumb impression.

And, if you want to check AIIMS MBBS seat reservation, you can go through the link below-

 https://medicine.careers360.com/articles/aiims-mbbs-seats-reservation 

Do let me know if you have any other query.

Good Luck!