I don't think you're understanding taxes very well. And your Dad doesn't get back money for you, he gets a credit subtracted from his income so there's that much less taxed. The taxes on a credit amount aren't that much.

But if you're making X dollars, supporting yourself, only you get to claim yourself, doesn't matter your age or that you're a student, etc. Literal IRS taxes and what your school is doing for your scholarships, etc. are not the same things.

http://www.irs.gov/individuals/students/index.html

But for your question, I would just, as matter of factly as I could, ask him for a certain amount of money, not go into details or be defensive or antagonistic about it or anything. That wouldn't get you the money. Be what he "wants" to get the money. You can revile him as a thief when there's not so much on the line and you don't need the money. When you're rich and famous you can not help support him :-) But just remember your goal for the moment is to get the money and play the charming little daughter role, daddy's girl.