Not sure what you mean but here is the code that should work:
--local script
local fdksod = game:GetService("ReplicatedStorage").RemoteEvent
fdksod:FireServer("Cat")
--Server Script
local fdksod = game:GetService("ReplicatedStorage").RemoteEvent
fdksod.OnServerEvent:Connect(function (player, string)
--do what you wanted with GUI using player argument. Argument string will be "Cat"
end)