Can I earn an extra point if you prestige in MW2 after you have already prestiged in MW3? I did and dont see the PP
Yes, you can get a prestige token in Modern Warfare 3, if you prestige in Modern Warfare 2, even now. Note that you can only get one prestige token per game - so if this was your second (or third, etc) prestige in MW2, you won't get another token for it.
Sometimes it can take some time for the point to show up; sometimes you'll want to log out and log back in, or wait a day in order to see the new token if you earned one. If you're still having issues, the best thing to do is to post on the Modern Warfare 3 forums for support.