To determine if an author is a historian, you can search for them in Google. If they are a living historian they will typically have a web site on a department of History web page or an author home page from a publisher outlining their credentials.
When assessing a book, read the author's biography on the back page of the book's jacket cover. Usually a "professor of history" is a historian, whereas a journalist would not be.
In JSTOR you can typically findarticles authored by historians by searching for professional book reviews and articles within the History category subject area.
Many peer-reviewed scholarly articles list the educational credentials of the author within the body of the paper.
How to best locate historiography articles?
When you are trying to locate historiographical articles make certain to add the search term
historiography to your search term(s). For instance enter the search string:
historiography AND prohibition AND United States
historiography AND carlisle industrial indian school