No one. That's one of the virtues of science.So who has a monopoly on the scientific method?
Of course it takes training not only in the basics of what is known, but how to conduct a valid experiment, how to evaluate the results, what constitutes evidence for a conjecture and so forth.
When I was studying Chemistry many years ago, I spend uncounted hours in various labs doing experiments designed to train me on such things. In graduate school I had a course that involved presenting results from a paper in the literature which included learning a deeper understanding of how to read such papers critically.