His performances in the musicals “Spring Awakening” and “American Idiot” are probably what John Gallagher Jr. is most known for (he won a Tony for the former). I ask him about two recent play productions (“Long Day’s Journey Into Night” and “Jerusalem”) that I suspect were very formative for him. We also talk about his latest screen role in the important and moving indie “The Miseducation of Cameron Post.” And, of course, I couldn’t let him go without talking about Sorkin.