JoeF said:Law degree and specialization in immigration law.
And to be allowed to practice law, a person has to pass the bar exam.
In principle, it actually is possible to pass the bar exam without a degree. Some states allow that. It is very hard to do that, though.
I recently came across an article about a woman who managed that. If I remember right, her mother is a lawyer, though, and so she knew what to study.