You are resetting your count to 0 each time you run the method. Quickest fix is just declare the variable outside the method:
int scoreCntr = 0;
void matcher_GestureMatch(Gesture gesture)
{
lblGestureMatch.Content = gesture.Name;
scoreCntr++;
var soundEffects = Properties.Resources.punchSound;
var player = new SoundPlayer(soundEffects);
player.Load();
player.Play();
lblScoreCntr.Content = scoreCntr;
}