Condensation on Skylight
Just a layer of shrink wrap will be fine , as long as you prevent the moisture from getting up to it it will quit sweating. 

Make sure to run the exhaust fans in the bathroom when bathing or using hot water to shave, also run your exhaust when cooking. 

I found some really good stuff for sealing windows in the past that you put on the frame and shrink it with a hair dryer, I hade to make a “picture frame” and mount it as I had no trim mine was all Sheetrock. I made a frame put the film on it and then used finishing nails to hold it in place you can barely see the film , I thought I might take it down in the summer but it has been place for almost 5 years now 
The stuff I used was 3m for insulation but I don’t remember a name.