Are you joking? My guess - less than 5%. In big cities maybe 5-7% in the best case. I know English better than most of my aquaitances, but still, when I watch an American movie without subtitles/dubbing I understand less rhan 50% .
Well I also do not understand anything when I see an English-language movie or listen to a song.
At the same time there is hardly 1% who can read English as I can so the number of those who can understand a move is even less.
Well I count all the age groups. I think the least percentage of understanding is among the schoolchildren and among the old people. For the middle age and the students the percentage is greater.