Who is the protagonist in The Magician's Nephew? Who is the antagonist?
To find the protagonist of a story or novel, think about whose problem or goal the plot revolves around. In The Magician's Nephew, the story begins with Digory Kirke crying about his mother's terminal illness. Digory is the one with the problem, and his problems only escalate throughout the story until the climax, when he makes the right decision. In the falling action, Aslan gives Digory an apple to take to his mother, and his mother recovers. Thus, Digory is the protagonist.
The story has two antagonists, Uncle Andrew and Queen Jadis. To find the antagonist of a story, look for the character who works against the protagonist, interferes with the protagonist being able to achieve his goal, makes the protagonist miserable, or puts him in danger. At the beginning of the novel, Uncle Andrew, a would-be magician, experiments on Digory and Polly, Digory's friend. He coerces them into putting on the magic rings, which he thinks will transport them to another world. He is too cowardly to experiment on himself. This sets Digory and Polly on their adventure, where they meet the fearsome Queen Jadis. She wreaks havoc in several worlds and eventually presents Digory with his biggest temptation—to steal an apple from the tree. Andrew remains a bumbling, groveling sidekick to the Queen, but becomes the lesser antagonist as the novel progresses and because Jadis poses the greatest threat to Digory.
Polly is Digory's sidekick, accompanying him on his adventures.
C. S. Lewis created a wonderful tale of adventure featuring a sympathetic protagonist and antagonists that readers love to hate.
An interesting question. The protagonist is fairly straightforward; it is Digory Kirke, the magician's nephew who gives the novel its title. It's his core adventure—he whose mother is ill, he who has to face great temptation with the fruit that could heal her, and so on. He's the character who the story focuses on, and who goes through the greatest growth.
As far as antagonist, I'd argue that there is more than one. I'd say that Uncle Andrew and Jadis are both antagonists at times; that's who Andrew must contest with. Polly goes back and forth between being helper, foil, and antagonist.