Undergraduate history students are usually required to complete different courses spanning from ancient Egypt to the Cold War. But given the vastness of history, it is impossible to memorize and keep in mind all the significant events that changed mankind. It is likely that by time you reach your 20th century history lessons, you will have already forgotten the name of the last Egyptian emperor. If so, are professional historians required to be good at or knowledgeable in all areas of History?
Professional historians are expected to demonstrate research capabilities. And mostly in one or two narrow specialties of history.
For most graduate programs, there is no "comprehensive" test or "common core" curriculum that one needs to pass. Historians do have to submit PhD dissertations, but those are "research," not "general knowledge" works.
Historians need to specialize in a specific area and time to make a contribution to research, and to generalize well enough to see patterns where they affect their area of research.
Recently I talked to a software developer over lunch about recent politics in Europe and I mentioned the Russian Civil War. and the Allied intervention. He knew neither the war nor the intervention. Perhaps that is excusable in a software developer, but for a historian that would be a poor showing.
Just memorizing the names and dates is pointless. Knowing what historical figures did and in what order is priceless.