easiest, would be to have the object in an extra family. ie object player in family "Checker"
tmpUID = 0
on click player
sub event: tmpUID = 0 ?
-action: set tmpUID = player.UID
pick all checker
pick checker by evaluate checker.uid = tmpUID
-action: set text to: distance(player.X,player.Y,checker.X,checker.Y)
-action: set tmpUID 0