You will not be able to see the door check mount. That part is located inside of the frame box in that area, your best bet is to remove the interior kick panel, then possibly find and manuver the fallen mount out through one of the access ports used by the wiring and vacumn lines to the door. If there is not enough room to fish out the mount you may need to enlarge an opening that exists or create one. If you do that you can then get the mount out, prep it and then attach a wire or string to get it back up into position inside the frame box to reattach it.

Before I did any of that I would get hold of a flexible stalk magnet ( check Samstage Sales, they have a 500 gram Sthalwille magnet that is very nice, smal and flexible, about $15) and try to fish the loose mount through the hole where it was mounted. If you can get it back into position you can get a wire or string attached to it. Once you do that, I'd drill a couple holes in the frame box, pull the mount into position and weld it into place using the holes you drilled sort of a replacement of the spot welds that originally secured it.