As long as the ball isn't in motion and it is on the green, you can mark its position and wait your turn to play.
Actually yes you can it depends were your ball lands on the green
Yes you can mark a ball anywhere except in a sandtrap
yes you can
No, you may only mark your ball when it is on the green.
mark your ball pick it up wipe it put it back pick ball mark up no stroke penalty.
They mark their ball out of courtesy for other players as if one player on the green hits the ball of another they receive a two shot penalty. It is also so the player can clean his ball and line it up.
You take a penalty stroke if you did not let te other player mark their ball.
Once you are on the putting surface i.e the green, you are permitted to mark your ball, clean it and replace it.
Yes, this is perfectly legal. You mark your ball, usually with a coin or marker. You can pick the ball up, clean it and replace it in it's original spot. The putter green is the only place where you can do so.
Basically, anything flat. Many golfers use a coin.