When you tow a cargo trailer is this insured under the auto policy of towing car?

It depends on the specific terms and conditions of your auto insurance policy. Typically, personal auto insurance policies do not cover damage to trailers or other towed vehicles. You may need to purchase a separate trailer insurance policy or an endorsement to your auto policy to cover the trailer. It's important to carefully review your insurance policy and speak with your insurance provider to confirm the coverage for your cargo trailer.