Bought a ninja as a project, and I'm trying to figure out what's wrong with it. After all the normal cleaning and replacing of parts I tried to start it up. But nope, it refuses to.. I pulled the plugs out after trying to start it and there was a little bit of black stuff on them (maybe oil?) and after a while of turning it over it starts to smoke out the exhaust. very thick white smoke, almost smells like electrical smoke. is there anything electrical that can smoke out the exhaust? or is it more likely that the piston rings need to be replaced and it's oil burning? The bike won't start and I think this is part of the problem.

I would do a compresion test and a leak down test on it. They will tell you a lot about the condition of the top end

There is lots of things that can cause oil to get into the cylinder, but by your description (thick white smoke) your head gasket is the most likely cause. Drain your anti-freeze and look for oil in it, drain the oil and look for water. It could also be the valves, valve guides, spark plug gaskets (was there oil in the spark plug holes?), bad rings and everything else on the top  end.

I hope you bought this Ninja at a good price, because it sounds like a helluva money pit.

new head gasket, and a new carb and it ran fine. lol. the carb was broken.. slide wouldn't slide... got it running and sold it for a huge profit. well worth it. and yes I got it for a steal.