Schedule 1, Line 21 - Student Loan Interest Deduction

For rules see NTTC 4012 page E-17. Note that in some cases a taxpayer can claim this adjustment when their child was the student.
Even if payments are made by others (say, a grandmother), for tax purposes the payments are treated as paid by the taxpayer. http://www.sheknows.com/parenting/articles/988817/parents-pay-student-loans-and-give-child-the-deduction
If the taxpayer doesn’t have Form 1098-E, Student Loan Interest Statement (lenders must issue this when the interest for the year is $600 or more), other information from the taxpayer is acceptable.

Only interest paid is deductible; repayment of principal is not. If the taxpayer doesn’t have a Form 1098-E, then determine how much of the year’s payments were for interest (not repayment of principal).
The taxpayer cannot take this adjustment to the extent that student loan interest was paid with distribution from a tax-free 529 plan or an employer’s educational assistance program.

Enter interest paid on the Student Loan Interest Deduction page [Deductions > Adjustments > ....]
More information, if needed, can be found in Pub 970, Tax Benefits for Education.
Note for CA returns: Student loan debt canceled or repaid under the Income Contingent Repayment plan, the Pay As You Earn Repayment plan, and the Revised Pay As You Earn Repayment plan as administered by the U.S. Department of Education, is also excluded from gross income by CA.