FlightRadar24 has released a new tool allowing you to see where GPS jamming is active

https://www.flightradar24.com/data/gps-jamming

It works by aircraft measuring the strength and quality of the GPS signals they receive when travelling, and then broadcasting this data which is then picked up by FlightRadars network of receivers and fed into the system. When there is no GPS interference, aircraft will usually get a decent signal. These areas are marked green on the map. If aircraft are getting a very weak signal, or struggling to get one at all, that could suggest there is jamming in the area. It doesn’t mean there definitely is, because there are a number of other reasons why an aircraft might be struggling to get a signal. For example, their equipment could be damaged. But if FlightRadar sees that multiple aircraft in a specific area are all having trouble getting a signal, they mark that area as red as that is more suggestive of jamming rather than faults with the individual aircraft.