If you purchased a digital version, search your inbox for the confirmation email sent at the time of purchase.
If you are reinstalling because you are migrating computers, but the old computer still has a functioning copy of Studio 12, you can often find the key within the "Help" or "About" section of the software menu.
Search for "Pinnacle" or "Avid" in your inbox. If you purchased a digital download years ago, the receipt will contain the key.
– they are common vectors for viruses.
It’s easy to mix these up, but they serve different purposes: