If you're talking about the cap that screws on the top of the plug, there shouldn't be one. It wont fit the connector with it on. If the plug isn't firing, check to make sure it's getting a spark to the plug. Make sure all your switches are on first. The sidestand switch, the kill switch and the clutch switch. Personally, I would just grab ahold of the plug, ground my hand to the bike and kick it over easily. If I get a shock, it's the plug. If not you need to look farther back up the wiring.
Bare