I want to co-sign on a vehicle for my daughter. I'm on medical and get food stamps. Will I lose my benefits if I sign?

You may not be able to sign based on other reasons. Like being judgement proof. But it wouldn't affect your benefits as the car isn't yours and it still requires payments to be made on it.

You can sign, but the issue is, why would they let you, since you have nothing for them to come after.

A person who co signs promise to pay if the other person does not, it appears you could not. Would they even let you co sign

Have you been approved as a co-signer? I think you will find you won't be allowed to. Lenders want co-signers with BETTER credit than the signer.