hi,

see while you registered for any particular bachelors or graduation level program or higher study course in any university, you would be allotted a unique registration number and roll number which you have to mention in all semester exam and it would be mentioned in your graduation mark sheet.

so you have to mention it while filling the application form. follow the official brochure and read it carefully while filling the form:

https://cetpg.puchd.ac.in/pdf/PU-CET-2021.pdf