If you cosign an auto loan for someone and that they have an accident and do not have car insurance will you be held responsible as well as the owner?

YES, you are responsible for anything that concerns the loan you co-signed.

In the land of litigation, anyone can sue for almost any reason. However, a lender would require insurance be carried on an auto until the loan is paid in full. Most states have insurance requirements also. The fact that he was uninsured could be a serious problem in the liability and legality arena. The transaction might be seen as fraudulent. What you knew or didn't know about this, might decide your responsibility (if any).