How do I give the player who killed 10points?

I'll give you the nice side of me and say that you did try.

Tag the player on hit.

Then, when a player dies, connect to a humanoid.Died signal to give the player points.

game.Players.PlayerAdded:connect(function(player)
    player.CharacterAdded:connect(function(character)
        local humanoid;
        repeat wait()
            humanoid = character:FindFirstChildOfClass('Humanoid')
        until humanoid
        humanoid.Died:connect(function(died)
            local playerwhoKilled = character:FindFirstChild('TaggedByPerson', true)
            game.Players[playerwhoKilled.Value].leaderstats.Points.Value = game.Players[playerwhoKilled.Value].leaderstats.Points.Value+10
        end)
    end)
end)