What is the law in California re paying tax at restaurants?

If you purchase food, you ARE paying a tax. The question is really how the restaurant calculates its tax. Most will add it on after they give you the initial total. Some include it in the prices individually. You are correct that most restaurant workers don't know the law. They don't have to in this case. They just have to give their total sales and turn in a percentage of that sales as tax to the city, county, and State. They have auditors and accountants who do that for them.