My friend wants to travel with me on a trip to Detroit. The problem is he only has a 1951 convention travel document as he is an Iranian refugee and has been living in the UK for four years.
Also does he need any kind of visa before going?
He will need to get a U.S. visa, like any other foreigner without a passport from a visa-free or visa-waiver country. What type of visa depends on what he is going to the U.S. for; e.g. for tourism probably B2 or B1/B2.