I received a grant from an independent private institution for my college studies. I have to return the grant + interest now. Can I use this interest as a deduction?

It appears that your grant has been converted to a loan.  The rules for what qualifies as a student loan for purposes of deducting the interest are fairly liberal. See: 

https://www.policygenius.com/taxes/student-loan-interest-deduction/#what-is-a-qualified-student-loan

https://www.irs.gov/taxtopics/tc456

Thanks! I wonder what can I do if the grantor refuses to provide me with 1098-E because "it doesn't relate to us since don't provide student loans". The grant was used solely for educational purposes and otherwise classifies as a qualified student loan according to the IRS link that you provided. 

Even though you don't have a 1098-E, enter your interest in box 1 at that screen in TT, per the "What if i don't have this" link on that screen.