“The Most Unknown” could not have been a more fitting documentary film title for Jenn Macalady, a Penn State geoscientist who is featured in the film. Macalady had no idea that a series of interviews — some conducted below nearly a mile of earth at Italy’s Gran Sasso research laboratory — would lead to a documentary premiering March 16 at CPH:DOX, the Copenhagen International Documentary Festival. She even didn’t connect that the director, Ian Cheney, was one of the filmmakers responsible for “King Corn,” a documentary that impacted her early in her microbiology career.