How to tell VLC 2.3.0 to scan a local folder on an iPad
iOS does not expose its filesystem to apps, outside their own sandbox. As far as an app is concerned, the only files on the iPad (or iPhone, or iPod Touch) are its own files, in its own sandbox.

You can upload the files to VLC by either using 'open with' (from Dropbox or from other apps that expose the ability to open files in other apps), or by going to iTunes and copying the videos to the VLC app. This puts the files in VLC's own sandbox.