Dear candidate, 75 percent is required in class 12th to appear in JEE mains for general category and 65 percent is required for reserved categories. However, relaxation is given in this criteria this year due to persisting covid situation. For more information, you can check:

https://engineering.careers360.com/articles/jee-main-eligibility-criteria

To know about NIT cutoffs of different categories, you can check:

https://engineering.careers360.com/articles/nits-cutoff-for-top-btech-branches

Hope, it helps!