The Equal Employment Opportunity Commission has the mission of investigating employment discrimination. They also educate employers and others about the nation’s discrimination laws. They issue guidance to employers (and employees) on what discrimination looks like. The EEOC actually issues some very good, well-supported legal guidance. See this site for excellent articles on every aspect of discrimination. Those articles are for lawyers. For the layperson, see this site for general guidance.
Regarding discrimination toward immigrants, there is this website. This site provides various examples of what discrimination against immigrants looks like. One of those examples addresses discrimination against person based on his/her national origin:
Examples of potentially unlawful conduct include insults, taunting, or ethnic epithets, such as making fun of a person’s foreign accent or comments like, “Go back to where you came from, ” whether made by supervisors or by co-workers.
Yes, that is the phrase Pres. Trump used in regard to four female members of Congress. He said they should go back to the countries from where they came if they do not like this country. It apparently did not matter to him that all four women are United States citizens. Yes, if we could couple the President’s remark to some Hispanic person he had recently fired, we would have a grade A discrimination lawsuit.