You can check out so-called slang dictionaries. Slang is very relative to which part of America you're talking about. Sometimes a word or phrase starts out as local slang and then becomes national slang as it gains popularity, etc. I can teach you this in a class. Please check out my teacher profile and feel free to book a lesson :)

I've never heard about it. Slang changes every day. A group of two people can have their own slang. I believe a number of Ph.D. theses were written on the subject. But I do not think there is a person alive who knows all the American or even New York slang.

There are "slang dictionaries." And full-sized regular dictionaries, like the American Heritage Dictionary, include thousands of slang terms and label them as "slang."

There is lots of slang used in American english! Every 5-10 years, new slang words are introduced with every new generation. But that's ok, because only slang from the current generation is commonly used! There are two types of slang: 1. National: Most people will recognize this regardless of the state you are in. Here are some examples of nationally used slang: Jacked, stan, bruh, drip 2. Local. This is less important, because it is less common. A person from California might not use slang from New York. Here are some examples of local slang: Well (Tucson, AZ), Pop (North Dakota and Minnesota), Snowbirds (Arizona), Brick (New York) Sometimes local slang becomes national. For example: "to front" started in New York, but it spread to other states. Also, there is slang for specific ethnic groups. Blacks, Hispanics, and Asians have words they use. If you'd like to learn more America slang, sign up for a class and I'll be happy to teach you more!