Hello,

The institute registration number in this case is your hall ticket Number or it can also be called as your roll number through which you use to check your semester results. Generally, Institute registration number /Roll Number /Hall ticket Number are all one and same. If you don't received yet your provisional degree or any ceritifcate issued by your college,  then you can submit your final year exam marksheet to show that you're eligible for GATE. For more information regarding documents for application, important dates, eligibility, FAQs and important notices, visit the official website of GATE 2021 ,link given below

https://appsgate.iitb.ac.in/