Hi......is there any toilet(W.C) on the top of the wall of Juyongguan?(sorry)

Yes, you can find them there, but it may not be easy to find. It is suggested to ask the staff if you cannot find one.

Yes, there are a few toilets on top of the wall. However, they are not western toilets, but are "Squatty Potties", so you will need to be aware of that. At the bottom of the wall, there are restrooms with both types of toilets, but no toilet paper is supplied (this is true of most of China), so bring your own. Hope this helps! :-)