Attempt to index nil with 'Position'

Help and Feedback Scripting Support
1 
local player = game.Players.LocalPlayer
local RS = game:GetService("ReplicatedStorage")

game.ReplicatedStorage.KillEvent.OnClientEvent:Connect(function(victimCharacter)
	if victimCharacter then
		local killgui = RS.KillGUI:Clone()
		killgui.smoke.NameTL.Text = victimCharacter.Name
		killgui.smoke.Studs.Text = math.floor(player:DistanceFromCharacter(victimCharacter:FindFirstChild("HumanoidRootPart").Position)).." Studs"
		killgui.Parent = player.PlayerGui
		
		wait(2.5)
		
		killgui:Destroy()
	end
end)

I don’t know what to do.

2

victimCharacter might be nil can you show us the part where you fired the client?

4 
game.Players.PlayerAdded:Connect(function(player)
	player.CharacterAdded:Connect(function(character)

		local humanoid = character:WaitForChild("Humanoid")

		humanoid.Died:Connect(function()

			local creator = humanoid:FindFirstChild("creator") -- Detect the ObjValue 
			
			if creator then 
				local victim = creator.Value -- Name of the victim, once outputed as a remote event, it will become a Character.
				
				if victim then
					game.ReplicatedStorage.KillEvent:FireClient(victim, player)
					print("Executed!")
				end
			end
		end)
	end)
end)
5

you could also try

killgui.smoke.Studs.Text = math.floor(player:DistanceFromCharacter(Vector3.new(victimCharacter:FindFirstChild("HumanoidRootPart").X,victimCharacter:FindFirstChild("HumanoidRootPart").Y,victimCharacter:FindFirstChild("HumanoidRootPart").Z))).." Studs"
6

you’re passing the player Instance instead of the character
also you need to change the victim variable to

local victim = game.Players:FindFirstChild(creator.Value)
game.ReplicatedStorage.KillEvent:FireClient(victim, character)
7

its saying

Players.Player1.PlayerGui.LocalScript:8: attempt to index nil with 'X'
8

discard that, read what i said above.

9

this should be the new ServerScript.

game.Players.PlayerAdded:Connect(function(player)
	player.CharacterAdded:Connect(function(character)

		local humanoid = character:WaitForChild("Humanoid")

		humanoid.Died:Connect(function()

			local creator = humanoid:FindFirstChild("creator")
			
			if creator then 
				local victim = game.Players:FindFirstChild(creator.Value)
				
				if victim then
					game.ReplicatedStorage.KillEvent:FireClient(victim, character)
					print("Executed!")
				end
			end
		end)
	end)
end)
10

For some reason, it’s not giving an output, and not displaying that you killed someone.