there should be a glass window on the right side of the bike. I usually refill it till the window is about half way or a little more full when the bike is sitting level, not leaning over on the triangle stand. make sure you give the oil time to drain down and level out before reading it, and then check it again after running it for a few minutes. I just use a good quality like 10w40 weight oil, and change it regularly. not sure if all of that is exactly correct, but it is what I do and it has worked out just fine, Im sure someone will correct me if I am wrong.
Jim