Tuition reimbursement

If you can claim him as a dependent, you can claim a tuition credit for his education.  The American Opportunity credit is worth up to $2500.  Grad students are only eligible for a lesser credit (Lifetime Learning Credit) worth up to $2000, but requiring more tuition having been paid. 

There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related).  He can't be a QC, since he's over age 23.  The Other dependent (qualifying relative) credit is worth (up to) $500 per dependent and is non-refundable.  

A person can still be a Qualifying relative dependent, if not a Qualifying Child, if he meets the 6 tests for claiming a dependent:

1. Closely Related OR live with the taxpayer ALL year
2. His/her gross taxable income for the year must be less than $4300 (2020).
3. The taxpayer must have provided more than 1/2 his support

In either case:

4. He must be a US citizen or resident of the US, Canada or Mexico
5. He must not file a joint return with his spouse or be claiming a dependent of his own
6. He must not be the qualifying child of another taxpayer