Cam Sprockets marks not aligned at TDC

Here is what my bike is doing    clunking sound  

I remove the valves cover to check

Here is what i found

when the mark on the generator rotor is aligned with the mark on the crankcase cover,
the mark on both cam sprocket are not aligned. Would it be possible that the cam chain skip a tooth ?
How do i verify if the tensioner is doing his job? To me it look tight but im a newbie .

First of all, a newbie would never open up an engine to check valve timing, so you're definitely not one.

Secondly, it's difficult to gauge how far off the markings are from that angle.

What you need to do is back off the tensioner and move one cam by one tooth to see if the markings align better. Keep in mind that the markings rarely align perfectly, they just need to be close, so choose the alignment that brings them as close as possible.