Don't worry about finding 919 specific stuff, all you need that's specific to the bike is how to slide the tank back and prop it up. Otherwise, you're just tracing the plug wire from the spark plug back to the coil that powers it.
Sounds like you'll need a new plug wire, which may be easiest to get in a set. eBay might be your friend, or if someone on the forum like cloroxbleach4 has some spares lying around.
The problematic part won't be replacing the wire, that's super simple (unscrew the plastic nut holding it to the coil, pull it out, put the plastic nut on the new wire, shove it hard onto the coil's pointy metal prong, tighten plastic nut), but determining if the spark plug came out because its threads in the head are stripped.
You can probably figure it out by looking at the plug threads. If they're not damaged and a new plug threads in easily by hand with a spark plug socket on an extension, it may have just been vibrated loose.
If the threads look damaged and/or a new plug won't thread in cleanly and easily, you might be in for a costly repair that involves removing the head to install a threaded insert where the old threads were.