How to reactivate Google Chrome's pretty print?

I'm not sure what panel of DevTools you're looking at. If it's the Sources panel, you can manually enable or disable pretty-printing by clicking Format.

In general, if you see that icon anywhere, clicking it will enable or disable pretty-printing.

I just did the same thing because of the really poor UI there. There's another option before "never show" with no separator, which makes these look like "never" and "show" are 2 separate options, not a single "never show" one.

I did find the solution though. Shut down Chrome, go to %USERPROFILE%\AppData\Local\Google\Chrome\User Data\Default\ and edit the JSON file called Preferences. In it, find prettyPrintInfobarDisabled which will be set to true and change it back to false.