A few places will do this. A leak in the roof at the front end of the gutter can work its way down the windshield pillar. All mY XJ's have developed rust holes in the roof at the driver's side front corner. So can a loose or damaged roof rack nutsert. A leak in the windshield sealer can come out almost anyplace. A clogged drain or rust hole in the cowl vent can leak but it usually ends up on the passenger side. Door seals are another possibility, especially if your door is a bit out at the top.
This can be really hard to diagnose if you don't see it coming in. See if you can get underneath the dash and look for traces of entry, rust, etc. But water can enter one place and travel pretty far before it exits, so it can be difficult.
Once things dry out you might be able to get a strong garden hose and see what happens when you aim it at various places.
