Taika Waititi owes a lot of this awards season to his mother, Robin Cohen. She’s the one who first told him that he should think about adapting Christine Leunens’ novel “Caging Skies” for the big screen.

That suggestion eventually turned out to be “Jojo Rabbit.” Adapted from “Caging Skies,“ the film was written and directed by Waititi. It goes into Oscar night with six nominations, including nods for best picture and adapted screenplay.

The film centers on a young boy, Johannes Betzler (Roman Griffin Davis), in WWII Germany whose imaginary friend is Hitler, played as a clown-ish buffoon by Waititi. Things take a turn when the boy discovers his mom (Scarlett Johansson) is hiding a Jewish girl named Elsa (Thomasin McKenzie) behind a wall in their home.

For the first time, Cohen, a senior tutor at Victoria University of Wellington in New Zealand, is revealing why she brought “Caging...