Education expenses used for a tax credit or deduction

I am filling out my son's tax return (full time college student), i am being asked the following question when filling out Education Deductions :

Education expenses used for a tax credit or deduction...

Your total qualified expenses are XXX.  These expenses make your distribution of educational funds non-taxable.  However, if the person who claimed you as a dependent also used some or all of these expenses to claim an education tax credit, we need to know what amount was used for a credit because it might make part of the distribution taxable.

For example: if the person who claimed you as a dependent also claimed the American Opportunity Credit for these expenses (which applies to the first 4,000 of education expenses) you would enter 4,000 below.

Where (specific form/line) do i find the appropriate amount on MY tax return that should be entered here on my son's form?