While the story is set in France and Germany during the early 1940's, and while many of the events in the story result from circumstances of the war, I wouldn't call All the Light We Cannot See a WWII novel.
Marie-Laure is a young blind girl living in Paris when the German invasion forces her to flee with her father, who has been asked to carry with him a package that may or may not contain a precious diamond housed within the museum where he worked. When her father is killed in a raid, Marie-Laure is left to find her uncle and protect the museum's treasure.
Werner is an orphan living in a small group home in Germany when he is recruited into a special Hitler science program to develop his unique talents working with radio. Ultimately he is placed in a military unit whose job is to track down a legendary diamond.
But one more thing this book is not, it's not a story about tracking down a gemstone.
All the Light is very character-driven. It is a story about two remarkable young people and the relationships they develop with some other distinctive people in their lives. It is about choices, it is about surviving, it is about caring, it is about darkness and light. It is a complex and beautifully written story. This will likely be made into a movie that I doubt will do justice to the novel.... so I'd suggest reading it first.