Yes, behind the pillion seat. The website seems hard to check for different years of 636, but there is a link to e-mail them and ask.
The rack is totally solid -- I think I could lift the bike from a fall with it.
It attaches to the rear peg hanger mounts (2 large bolts) and under the pillion seat to the un-tidy tail (4 smaller bolts) -- I think they call it the "flap".