I find that using a thin putty knife, with some masking tape on the blade to protect the paint, you can insert it under the plastic and slide it along to find where the clips are. If they're like the other plastic clips found all over the interior, they are about a 1/2" wide, more or less flat in profile and snap down into a metal retainer. With the plastic now being quite old, don't be too surprised if you manage to break one, but you can minimize the possibility of breakage if you pry as close as possible to the clip. I recently watched a guy replace the windshield ('01 ST) and he had those plastic pieces off in seconds with no problem at all. Of course he's probably done hundreds of them.
Tip: Before reinstalling trim with those plastic clips, I like to put a dab of white grease in the metal clip to make it easier to get them apart next time. If those metal clips get rusty they're very hard to get apart.
RE the nozzle: IIRC the nozzle snaps into place on the bottom of the plastic trim piece. There are plastic grabber pieces molded into the trim piece that hold it in place. In my case the guts of my nozzle were missing and it would just puke washer fluid over the roof, LOL. If you find your nozzle "gabber" pieces are broken, you might be able to glue the nozzle in place with 3M yellow weather stripping adhesive or JB Weld. Otherwise you'll need to find a good replacement cowl trim panel piece.
BTW, I often look for photo's of parts I need to remove on eBay, as I find it helpful to figure out where bolts (in this case clips) are located.
