Can I, as the co-signer who made the payments on a student loan, deduct the interest indicated on the 1098-E.

Yes, if the student was your dependent when the loan money was used for education. 

You can claim the interest deduction, if you meet the three requirements:

1. You paid the interest
2. You are legally obligated to pay it (co-signing counts)
3. The student was your dependent, at the time the loan was used to pay for qualified educational expenses (the TT pop up says “when you took out the loan”)