If that play is based on Casablanca the movie, you'd be dealing with a black and white production from 1942. Considering the movie photography, which is the area responsible for how images will be delivered from the director to the audience, you will realize that light has a very dramatic approach in it.
The scenery is usually darkened then the first plan, which are the things and characters that are closer to our eyes. If we could draw a parallel between this movie and the art history, we would be able to consider that the director has chosen to use a similar technique we found in baroque paintings.
Many shades and a light falling upon the story climax.
A play tends to awake much dramaticity than a movie. As it aims to reach a distant audience, actors have to exaggerate their actions. The Italian Stage, which is the most scene technique adopted in Drama, was inspirational to many baroque painters, such as Carravaggio.
It will depend on your choice on how much dramatic do you want your scene to be? If you want to focus on the climax, a diagonal light, laid on actors, should be your choice. If you think that the scenario should be highlighted, you must enlight the whole stage. As the exercise asks, choose a scene from the movie and try to analyze how light is operated in it. Then, decide how you imagine it on a stage, which is wider than a movie framework.
Try to compare it to other productions that you’ve seen. In my opinion, the light used in The Lion King Musical is a good example. Good luck!