If the QTP 1099-Q was issued to you it goes on your return. You can claim this even if he is not your dependent.
Just remember that earnings on the 1099 (not basis) counter the school expenses. Basically you can't double dip (your son and you for the same expenses). You have to determine if you can chose who claims his personal exemption. If he is still eligible for you to claim generally parent(s) benefit more since they are in a higher income bracket.
If he does not qualify as your dependent if the money went to pay eligible higher level educational expenses your still good - just don't claim his exemption. FInd out what eligible expenses he had and use the link below to track.
Are Distributions Taxable? (depends) The part of a distribution representing the amount paid or contributed to a QTP doesn't have to be included in income. This is a return of the investment in the plan.
The designated beneficiary generally doesn't have to include in income any earnings distributed from a QTP if the total distribution is less than or equal to adjusted qualified education expenses (defined under Figuring the Taxable Portion of a Distribution , later). Link for figuring taxable portion (if any) https://www.irs.gov/publications/p970/ch08.html#en_US_2015_publink1000178534
