Roof leaks can be hard to find, since they often run down the underside of sheathing or rafters to show up far from their actual source. The best time to try and find a leak is when it’s raining outside, or you can also mimic rain conditions by spraying water on the roof.
Go in the attic and look for damp spots or water stains, trace them back to their highest point, then examine that part of the roof for any potential problems.