Yes some items may ask for a license key, registration code, etc.
In most items you can enter anything you want, or just ignore it. License key is required for automatic updates of the item only. The item will still work even if you do nothing.
But you can't do auto updates when there's a new update notice. You have to download the latest version from GPL WP and install it manually again. Please refer to this article on how to update a theme or plugin.
Or, f you want to hide that notice, you can use this plugin:
* If you still have any questions regarding this topic, please post a comment below instead of submitting a new ticket.