Most of the places that you would probably find of interest have either closed, been torn down, or have been utterly remade. The most infamous site that I recall was the Broadway clothing store which is where Demetrius Holloway was removed from the planet in 1990. That was a shock if only because I had been to the store once or twice. But that store has closed now I think.
These two sites have some suggestions. Eastern Market is likely the only place which would still have some modern ongoing mob/mob related ownership here or there. Some mobsters used to stay at or own a piece of the Book Cadillac hotel.
Detroit Mob Historical SitesDetroit Sites WIth Mob Stories