where do I find my Office Product Key?

It depends if you are using Microsoft Office 365 or you purchase the product key, take a look at:
https://support.microsoft.com/en-us/office/using-product-keys-with-office-12a5763a-d45c-4685-8c95-a44500213759
https://support.microsoft.com/en-us/office/where-to-enter-your-office-product-key-0a82e5ae-739e-4b92-a6f4-2ec780c185db
In case Office pre-installed in your company's device or you are using a device connected to your company, you have to check with your IT department.

Which version of Office is in use?

See these links:
https://support.microsoft.com/en-us/office/find-your-product-key-for-office-2007-fabe03d9-fbc3-452e-8fd4-d1c2e661d518
https://support.microsoft.com/en-us/office/find-your-product-key-for-office-2010-1e8ef39c-2bd4-4581-a0ae-5cf25ebed489
https://support.microsoft.com/en-us/office/using-product-keys-with-office-12a5763a-d45c-4685-8c95-a44500213759#bkmk_viewkey

There also may be useful information using third party software:
https://www.belarc.com/products_belarc_advisor

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@Jacob Balva

Could you please let us know which version of Office do you have?

Reza-Ameri and Docs-4663 have provides some reference links, you may have a look first.

On devices that have installed and activated Office, we can find the last five characters of key. If necessary, you could try it.

Search CMD, right-click the Command Prompt and run as administrator. Then copy and paste the command in it, click Enter at last:
cscript.exe "%ProgramFiles%\Microsoft Office\Office16\ospp.vbs" /dstatus

(If you are running 32-bit Office on a 64-bit operating system)
cscript.exe "%ProgramFiles(x86)%\Microsoft Office\Office16\ospp.vbs" /dstatus

If you still need help on Office keys, I would suggest you contact Microsoft online, thanks for your understanding.

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