Extracting and Using Sensor in Camera Assembly of Nokia Lumia 1020
I've never done this, but here's how I would start:


find the data sheet for the camera.  If none available, I would find the most similar part with a datasheet available and start with that and learn all you can.
for this camera, make an interposing board with male and female of the camera connectors, and breakouts for a logic analyzer.
capture waveforms during a capture of a bright scene and dark scene
stare at waveforms for a long time.


You should then be able to blindly copy what the phone does to the camera.  Then you can use French cafe techniques to figure out what the registers do.