How do I find the source of a water leak in my sun room?

What type of water leak? From pipes? Or water intrusion from improperly graded landscaping?

How is the water getting in?

Where is the leak? What is leaking?

Water can run along a solid surface for several feet before showing up as a spot on the ceiling. Here is an article that details what to look for: https://www.familyhandyman.com/roof/roof-repair/roof-repair-how-to-find-and-fix-roof-leaks/view-all/

Older pipes can spring a pin-sized leak that may take a long time to show up. The longer a leak goes unnoticed the greater the damage. Is there a bath or kitchen on the other side of that wall? Is there a bathroom upstairs? How about a hose bib on an exterior wall? Check for a leak first by turning off your water supply at the meter. If your meter continues to run you have a leak. Check for dampness in the wall, on the floor, or in carpet at the base of the wall. To fix this you will have to remove drywall/plaster to get to the pipe that's leaking.

It's more rare, but sometimes the nail or screw that holds up a picture or cabinet can nick a supply pipe. The resulting leak could be immediate or take some time to manifest. An iron fastener doesn't have to put a hole in copper pipe; it just has to rest against the metal to cause electrolysis that weakens the pipe. Know where your pipes are before you decide to hang something.

Water leak in your roof?

Go into your attic and see where the water stain originates from. It may be away from where the stain is in your sun room. Sometimes you can see daylight shining through a small hole in the roof. If no attic, go on the roof and look at the shingles. Se if some are cracked, or not laying flat. Use roof mastic on those spots.

It's probably coming from a window find what window it's coming from look for water lines

You don't mention the degree of water intrusion, but if you turn on your hose and spray over the roof while another person is inside the sunroom's interior, I suspect you'd find the leak.

Did you check all attachment points between roofing glass? If not there, move down to windows. It may need caulking or flashing. Just because caulking looks o.k. does not meal seals are tight. Press on caulking to see if it flexes and shows signs of separation.

Try putting Damp collectors (Cheap) and see if that sorts the problem. It will if it is condensation? Otherwise look at the roof or re-seal around your windows.