There are so many places a trailer can leak water; also water can leak in in one location and then run elsewhere and do damage. All of which makes it tough sometimes to track down the source of the leak.
Is there any evidence inside - on the ceiling or a wall? You could look inside cabinets, or remove fixtures like lights and roof hatches to look for evidence.
Exterior hatches, access doors, windows and lights can leak. In fact any penetration of the sidewall or roof can cause a leak. Where different pieces are joined - as at the corners of a trailer, or where the roofing material joins the sides or ends - are all leak possibilities.
You could get a leak test done. This involves a dealer having the proper equipment who slightly pressurizes (with powerful fans) the inside of your trailer and then looks for air leaks with a bubble solution.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch