If your friend was pulled over without insurance, they would be the one to receive the ticket. However, if they caused an accident, the other party may be able to come after you AND your friend for damages. This is because you are the owner of the car and required by law, as an owner, to have insurance on the vehicle. It would be best to get at least liability insurance
. You can see what WI requires here.
Then you would be able to add your friend as a driver. If you do this, you will not have to worry.