The greatest literary memoir of the 20th century, Vladimir Nabokov’s “Speak, Memory,” ends with an emblematic image, that of Nabokov standing alongside his 6-year-old son Dmitri as they gaze at the ship that will carry them from France to safety. Over the preceding pages, the author has survived numerous losses and brushes with danger, fleeing not one but two totalitarian regimes: the Soviets and the Nazis. And while that memoir has many moving moments, none are more so than those dedicated to filial love — Nabokov’s love for his father, Vladimir Dmitrievich Nabokov, assassinated in 1922, and for his young son, Dmitri Vladimirovich Nabokov.