Paul Anthony Kelly shares how he prepared for his role as John F. Kennedy Jr. on the FX limited series “Love Story,” from learning to write and move left-handed to working with a dialect coach and studying Kennedy’s voice. He discusses filming emotional scenes with Naomi Watts (Jackie Kennedy Onassis), building chemistry with Sarah Pidgeon (Carolyn Bessette), navigating his first major role, and the perseverance that kept him going after 13 years of pursuing acting.