ORIGINAL: WRK
Have you tried to put the plug in the cap and ground the end of the plug (plug out of engine) and see if there is a spark at the plug electrodes when
you turn over the engine?
You might want to do this in a place where the light is dim.
No need to ground the plug to the engine. The ground return completes the circuit through the plug lead shielding. If the spark is good you should be able to easily see it in any normal light as well as hear it.