This is pretty easy. In a metro area with an ethnic area..... look inside.... if you don't see any white people, then that is a sure sign it's pretty authentic. Now if you want even more authentic, befriend someone and hopefully they take you back to their parent's place. (That idea is not intended for people of this forum with yellow fever
Or better yet, get a cookbook about the cuisine you are interested in. The better cookbooks should talk about the basic concepts for that particular cuisine. It will be your starting point. The whole idea is I think for you to have better understanding about the guiding principles for a cuisine so that you can replicate the concept, favors, aroma, texture, etc.