I already put a RemoteEvent in ReplicatedStorage.
LocalScript which is inside a Part in Workspace:
script.Parent.Touched:Connect(function() game.ReplicatedStorage.RemoteEvent:FireServer() end)
Script which is inside of ServerScriptService:
game.ReplicatedStorage.RemoteEvent.OnServerEvent:Connect(function() print("ok") end)

5 comments
super strange i put this script into the Part and it doesn't even work : script.Parent.Touched:Connect(function() print("touched") end)
Local scripts can't fire server events!
Your local script is in a character?
Localscripts won't run in workspace. They have to be inside playerScripts or a player's backpack. Use a script instead.
LocalScripts don't work in Workspace, and if you chose to use a Normal script, FireServer() can't be fired there, as you're already contacting the server. So, just put a Normal Script inside the part and write the function you want.