1) find another store. there's lots of stores.
2) launch a boycott.
i know i won't be shopping there any time soon.
at the end of the day, you can't force somebody to make you a cake and, in the absence of any sort of altercation (like being chased down the street and yelled at by thugs), there's not really any reason to award any sort of damages, but you can try to push the company out of business and have them replaced with a different one that will.
the idea that this person needs to be "educated" is rather dubious - they likely understood exactly what they were saying, and you're not likely to get anywhere by trying to convince them of anything. if it was a big company, you could maybe look at their training documents. but, in context, that entire discourse is really dubious. this person doesn't like drag queens and didn't want to draw a picture of one, and that's all there is to it.
so, organizing a boycott is the proper response, not trying to "educate" them.