Hello 
Just a little note… Previously it was enabled on my site but than I disabled it. Now I looked for the site setting show_copy_button_on_codeblocks to turn it on again. But it has been hidden. So the reason I write it is it seems if previously had disabled this setting it keeps the default: false status and can only be activate with rails SiteSetting.show_copy_button_on_codeblocks=true.