Below is a sample restaurant Comment Card for your reference. You may modify it as per your needs.

You ca ask about food quality, Menu Variety, Service, Atmosphere, Cleanliness and overall experience of the customer in your restaurant. You may also ask some additional questins like serving manners of the staff and the taste of food and the like.

Please do not forget to encourage customer to give feedback about improving the services of your restaurant. This will definately help you getting more quality of your food.