| The stacked knob is your bass/treble pot.
The first thing to try is find a precision screwdriver of the appropriate size and make sure the set screws that hold the knob to the shaft are tight.
You might also make sure that the volume knob isn't pulled up. Pulling it up defeats the tone controls.
As for the jack, I've read (here, mostly) that Warwick basses often have jack problems, so that may be the source of the random cutout.
If nothing I've said helps, either take it back to where you bought it, if it was from a store, or take it to a tech. | 
