It's a question used to ask someone what class they are preparing for, or what class something is intended for.
Here are some examples of how it might be used:
* ¿Para qué clase necesitas este libro? (For what class do you need this book?)
* Este trabajo es para la clase de español. (This assignment is for the Spanish class.)
* ¿Para qué clase es esta presentación? (For what class is this presentation?)
The phrase can also be used more generally to ask someone what they are preparing for, but it's more common when asking specifically about classes.