Your connection key is needed when the device is in Wi-Fi mode and you're using an online service, such as synchronizing the Handy to videos. This key is unique to your device, which allows anyone to control your device remotely, if they know your key.
Accessing key through handyfeeling.com
NOTE: Before accessing your connection key through handyfeeling.com, you will need to have completed the setup.
You can set up your device from here: handyfeeling.com/setup
On handyfeeling.com click on the button in the top right corner. You should then see the following popup. On the popup, there's a button to copy your connection key.
Accessing key through HandyConnect app
If you used the HandyConnect app in the past, you can also use it here. You can read more about the app here.
Once you connect in the app, you will see the following screen. As an example, the connection key is abcd1234.