ArcGIS PRO does not automatically include all fonts to the Resources\Fonts folder. The solution is to add/copy the fonts into this folder. Where do I get the fonts? Thanks.
If you're asking where you find the fonts already installed on your computer, that depends on the operating system.
For Windows, it's generally <C:\Windows\Fonts>. I don't know where it is for iOS or Linux.
I don't know that I've ever had a problem with ArcGIS Pro seeing the fonts I have installed there. Are you running into problems with it not recognizing the fonts?