Yeah, when I posted I assumed that was a "scott" original bracket and assumed (incorrectly) they wouldn't be so dumb as to leave you without a dipstick.
I'd probably make a dipstick - do a normal oil change, and fill up with the correct, measured known quantity. Run the bike for a little while, then make a dipstick out of a coat hanger or something similar. Piece of tape to show a known spot, stick it in the open filler hole down to your mark, and pull it out. Whatever it shows is likely to be pretty close to the normal mark so use that as a reference going forward.
Stock dipstick is pretty much a 6" or 7" straight rod, but none of that matters as long as you have some kind of reference and you use it the same way each time.