You've got a few problems.
First, in Java you need to declare the length of the array before assigning values to the array.
Second, your code was attempting to set the text of the label before the label was assigned to the array.
Third, you were using a variable that didn't exist (Singleplayer
).
Try the following changes and see if you can go from there...
private JLabel JSingleplayer [] = new JLabel[10];
for (int x = 0; x < 10; x++)
{
JSingleplayer[x] = new JLabel(PlayerName[x]);
// the following assumes you've also declared EndPanelscore...
EndPanelscore.add(JSingleplayer[x]);
// you have similar problems here...
//JSingleScore[x].setText(SingleScore[x]);
//EndPanelscore.add(JSingleScore[x]);
}