Can—or should—evil be understood? For John Boyne, Ireland’s highly successful novelist, this question could not be more personal. And yet, his tone when writing on the subject is cool and distant, almost conversational. It’s like he’s inviting us to contemplate, alongside his characters, the unthinkable. That’s likely because he did, too.  Meeting Boyne, who is jovial and smiling, is much different. We sit in a bright, high-ceilinged rom of the Penguin Random House offices on Nassau Street, where he beams between personal anecdotes (“one of my earliest memories is getting my tonsils out, because my brother needed his out and…