If you have purchased Serato Video or upgraded your license from Video-SL, the license is registered to your Serato.com profile.
To access the serial number, log in to your account, then click on "Profile" underneath your username, which will take you to your profile page.
Directly underneath your username on the profile page you will see "Products" which will then take you to a list of your registered products.
Clicking on the "Show Serial Numbers" button, then entering your password, will then reveal your serial number for Serato Video.
Note: If you have purchased your Serato Video license in a bundle (for example, with Serato DJ) you will not see the serial number here as you do not need it to log in. Please sign into the MY SERATO panel inside the software with the account you used to purchase the licence to activate Serato Video.