Cannot locate scanned document from printer on iPad

First you need to understand that AirPrint is a driverless printing protocol - this being used to print from your iPad to the printer. This protocol does not support scanning or other functions of your multifunction printer.

Non-printing functions of your multifunction Printer (e.g. the scanner) cannot be natively accessed by your iPad - as these additional functions require installation of appropriate device-driver software on the iPad (as would also be the case when using other computers with which you may be familiar, such as an Apple Mac or Windows PC).

iOS/iPadOS does not provide a method of installing device-driver software other than by installing a companion App provided by the printer manufacturer. For HP Printers, to scan documents directly to your iPad, you'll need to install and use the HP App - this being a free download from the Apple App Store:

https://apps.apple.com/gb/app/hp/id469284907

if it was me then I would check camera roll and if not there then I would check hp's support as to where they store scanned images.