Add nephew as dependent?

If he is eligible under the Qualifying Child rules you should be able to claim him as a dependent and enter the education expenses you paid for him on your tax return.

In the My Info section you would select Other person for dependent type and from the dropdown choose Nephew.

To be a Qualifying Child -

1. The child must be your son, daughter, stepchild, foster child, brother, sister, half brother, half sister, stepbrother, stepsister, or a descendant of any of them.
2. The child must be (a) under age 19 at the end of the year, (b) under age 24 at the end of the year and a full-time student or (c) any age and permanently and totally disabled.
3. The child must have lived with you for more than half of the year. Temporary absences while away at college are considered living with you.
4. The child must not have provided more than half of his or her own support for the year.
5. If the child meets the rules to be a qualifying child of more than one person, you must be the person entitled to claim the child as a qualifying child.
6. The child must be a U.S. citizen or U.S., Canada or Mexico resident for some portion of the year.
7. The child must be younger than you unless disabled.

That's complicated.  To be your dependent, he must meet of bunch of tests that @DoninGA posted, but I'm going to focus on the "must live with you more than half the year" test.

Because, even if he lives with you, his parents may also be able to claim that he lived with them more than half the year.  He can be considered to live with his parents if he would have lived with them and was away for a "temporary absence"--and education is considered a temporary absence.

So if he would normally be living with one or both parents except for college, then that parent can probably claim he "lived with them" and claim him as a dependent and claim his expenses.  If you also claim him, I don't how the IRS would rule on the dispute--would the parent win, or would the aunt where the child actually lived win?

If there is no other person who could might try to claim him as a dependent, such as a parent, then no problem.  But if the parents are involved, you might need to have a conversation with them before you file, because if you both claim him, you will both be talking to IRS eventually.