How do I view a scripts source-code?

I've tried to do ;

print(script:FindFirstChild'Source')

To put it simply, you cannot.

ROBLOX locked the Source property of Scripts to stop exploits that involved them, and they will never open them again. To access the contents of a script, you're going to have to use a StringObject, and paste the script into it.

Roblox has RobloxLocked the source property of scripts. This update prevents players from reading, modifying, removing, or adding snippets or in full of the source code due to exploiters and other Roblox Security reasons. So with that, your script will error out all the time unless the script you want to copy code from follows loadstring (off by default due to Roblox Update), and listens to a StringValue called "Source" in which case it should be script:FindFirstChild("Source").Value