(Branched out as a new thread)
As you have mentioned you need to find the serial number for Photoshop CC, Creative Cloud apps do not require a serial number they are activated with the help of the registered Adobe ID's (email address) to know more kindly refer to: Learn how to activate and deactivate Creative Cloud apps.
If you have an older version of Adobe Photoshop, then you may refer to: Find your serial number.
Let us know if you have any more queries.
Simply subscribe, no serial number is used.