Hi:
The W10 product key should be in the BIOS and is not needed to reinstall W10.
If you look under the Activation section of the Update and Security menu in the PC Settings, it should show that Windows is activated.
If you want the original operating system that HP installed on your notebook that includes the drivers and software that it originally came with, use the HP cloud recovery tool to create a bootable USB recovery drive that will reinstall those items.
Here is an info link for how to use the cloud recovery tool...
https://support.hp.com/us-en/document/c06162205