How to get raw values from the MPU9250 Magnometer sensor or "AK8963"

No idea, but why would you or anyone else want one? The newer 9DOF sensors all significantly outperform it, and if purchased from a reputable supplier, are guaranteed to work.

Cheap sensor modules of the "GY-" variety are throw-aways built from obsolete, clone or substandard parts, intended for hobbyists having fun putting things together on a breadboard, not for any serious use. They are often sold in multiples, so that there is a good chance that one or two will be fully functional.