PK Finder is a portable tool which detects and displays your Windows product key. The developer says Windows 8-10 are supported.
Simply run the program and it immediately displays your Windows version and edition ("Windows 10 Home"), along with the product key.
Tap a button and the key is copied to the clipboard. Alternatively, clicking File > Save saves it in a text file.
The developer has also included assorted interface settings, including a choice of "Style" (Metro, Office, Transparent, VS2010 and more), colours and "border thickness". Seems like overkill considering most people will barely use the program once a year, but the feature is there if you need it.
PK Finder has better visuals than other Windows product key finders, but we're finding it hard to care, and if you agree, there's no reason to choose it above any other key finder.