The first thing to check is if you are getting spark. You dont need to pull the plug, find an old plug of anytype and plug it in, next ground the plug to the motor and give it a crank. If the plug sparks than suspect the plug itself. This can also be done if you have a timing light and you can it that way. Keep in mind that a spark plug will rarely just stop working while running. Normaly it will backfire or run like crap before it stops. If there is no spark, there can be several reasons. YOu will need a multi-meter from here on. Download the service manual, it will make this easy. Check to make sure that there is voltage going to the ignition system. Remember that there are two safety cutouts on this scooter, the one of the side stand will kill the motor if its running. If this failed, it will stop the bike while running as will the like mentioned before the kill switch on the handle bars. Electrics are no fun but with a multimter and a little time, they can be fixed on your own.
Good luck,
EZ