To get the product key that we have running on our Windows 10 just have to download a program that we can find in this link
Once inside, we go down to the bottom of the page and find the download links for the program in question. By the way, its name is "Product Key".
As our Windows 10 is 64 Bits we will click on the link where it says "for x64".
Click on the download below on the left
We'll decompress on the desk.
Double click on the icon you have selected.
Et voilà! The activation key appears, that is to say, the product key that we introduced in its day to activate Windows 10 when we installed it.