I,m pretty sure it,s the cam chain adjuster. Don,t know if it,s broke or not. I,m not at all familiar with the DOHC,s I,m just going on the look with the bolt and jam nut which is used on the SOHC, Sorry not much help.
Look at the bottom center of the first page in the link... shows the tensioner, bolt, locknut... and what looks to me to be a plug/seal that would go in the hole in front of the engine.
Item 19 is a plug that looks to be missing on your bike. If the link doesn't work for you just go to Bikebandit.com and look at the cam chain tensioner detail.