The drains are probably located at all 4 corners of the drain pan around the sunroof. The front ones drain down the windshield posts, the others down the posts at the rear of the front doors. Sunroofs are NOT waterproof!

It is quite common that they clog up.

I use a stiff, insulated wire to clear drains - make sure that whatever you use has no sharp parts.

Do not get aggressive with power equipment - you can damage or dislodge the drain tubes, which are pretty old now.

After you clear the drains, you can check them by pouring a glass of water down each one and see it coming out the bottom. I do this about every two months - the sunroof can pass water summer and winter.

If you have a sedan, there might be drains in the front corners of the trunk - check with a glass of water. Also check the rubber strip at the front of the trunk, as debris can cause a leak.

Have you checked your door drains, your rocker drains? If they are damaged or clogged, they can cause rot that will lead to the end of your car.