As Hal_Al pointed out that credit is not available for Grad School, but you may qualify for the Lifetime Learning Credit.
Here is a link to those qualifications: Life Time Learning Credit .
[Edited KarenM90 4/4/2020 3:47 pm pst]
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Q. I am a 2nd year graduate student. I have never claimed the American Opportunity Credit (AOC) (I think my father did when I was living with him), can I claim it now?
A. No. The AOC is not available for graduate school education. Even if you were still an undergrad, you would have to determine how many times your parents claimed it on you. There is a 4 time limit, per student, not per taxpayer.