Nowhere. In fact, there's a Supreme Court ruling on it (Brandenburg v. Ohio). However, this same "trolling" rhetoric has ended up in the screeds of many mass shooters, like the one in Christchurch and, by extension, the one in El Paso. Inciting violence is the only exception to that ruling, and thus is NOT protected by the First Amendment.
But remember, there is precedence for Supreme Court rulings to overrule previous ones, and the same with Amendments.