[I'm a cofounder at Hack Reactor, a coding bootcamp.]
Your comment defines a trade skill as one "that most anyone should be able to learn in several months without a general STEM education". So, let's evaluate that question for a few different trades/professions.
"Software Engineering": We have determined, through experimental proof, that bootcamps can make (some) novice non-degree-holders into employable software engineers in 3 months. Probably 3-18 months would cover most people that would otherwise be entering college in a CS major.
At parties I like to ask people how long it would take to teach someone to do their job. (Posit that they're smart and interested.) For most white-collar jobs, people answer "6-18 months". Most trade schools are somewhere in that region as well.
In my opinion, most professions would be well-served by the bootcamp model (like software engineering is) and a 6-18 month training period. So per your definition, I would say there are few professions out there, if any.