I recently had a break in and faced the replacement of this window. I
found the glass for $35 so I thought I would give it a try. I
couldn't find any resources in my Haynes manual other than "remove the
glass", or anything online. So I finished the repair myself and
decided to share my insight.

The inner door liner has to come off so the sliding window can be
removed, this is discussed in the haynes or other manuals decently. I
had to remove the window from a junk car with no window functionality,
what a nightmare. I can't remember if the outer lower sliding window
trim needs to come off, I broke the forward mounting point because I
didn't realize it was bolted from the inside of the door. Leave it
alone for now. The sliding window rubber molding/race can be pulled
away from the vertical divider and pushed out of the way to make it
easier to move the vertical divider. The vertical divider is fixed in
3 places: 2 nuts on inner door panel frame, and 1 screw which is
accessible from underneath the weatherstipping on top of the door.
After this vertical divider/race is pushed sufficiently forward (front
of car) the new vent glass in its rubber molding can be squeezed into
the space. Then just get it snugged into place and start fastening
the hardware back into place.