I believe the clips that hold the windscreen cowl panel in place are push pin clips. They are a two piece construction with a pin in the center of the clip you pull out to collapse the diameter of the clip, or push in to expand the daimeter of the clip. You have to pull the pin out, line the holes in the cowl to the holes in the sheet metal, push the clip into the hole, and push the pin into the clip. By pushing the pin in, you expand the clip and it won't pull out of the sheet metal.
By the way, sometimes the easiest way to extract the pin is to push it through the clip, remove the clip, retrieve the pin, and re-insert the pin in the clip. Don't do this is the pin will drop into an area you can't get at.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)