i want to make a gui appear when teleported but the gui doesnt appear, how do i do it?

It's NOT a localscript the error code: attempt to index nil with 'PlayerGui'

The script

function onClicked()

	local c = game.Players:GetChildren()
	for i = 1, #c do
		c[i].Character.UpperTorso.CFrame = CFrame.new(script.Parent.Parent.Teleport.Position)
	end
	
	player.PlayerGui.Tasksbar.t1.Visible = true -- the gui
	player.PlayerGui.Tasksbar.t2.Visible = true -- gui
	player.PlayerGui.Tasksbar.t3.Visible = true -- gui

end

script.Parent.ClickDetector.MouseClick:connect(onClicked)

####Re-edited by JesseSong!

The problem is that the variable "player" isn't defined. There are several ways to get the player, there is 1 main one for the server and another one for the client, to access the player on the server you can add a players.PlayerAdded event to your code, or if the code is on the client use game.Players.LocalPlayer. Also I recommend not using :connect since it's deprecated use :Connect instead.

You don't have player properly defined, fix:

function onClicked()

    local c = game.Players:GetChildren()
    for i = 1, #c do
        c[i].Character.UpperTorso.CFrame = CFrame.new(script.Parent.Parent.Teleport.Position)
 c[i].PlayerGui.Tasksbar.t1.Visible = true -- the gui
 c[i].PlayerGui.Tasksbar.t2.Visible = true -- gui
 c[i].PlayerGui.Tasksbar.t3.Visible = true -- gui

    end

   
end

script.Parent.ClickDetector.MouseClick:connect(onClicked)

Because you're getting a table of players and referencing an index for each player, therefore c[i] represents the current player, so you can adjust each gui like that.