What Code Does Prehook Install on My Store?

Prehook does not automatically add any code to your website.

The only code that Prehook will add to your store is the code that you Copy/Paste to install the quiz.
It will be added at this stage, in the Install step:

If you opt to Uninstall Prehook, and want to ensure that you have removed all code from your store, simply go to any page where you have pasted the code, and delete it.