Register with Wolfram Alpha's developer portal.
After signing in, you should see a dashboard overview with tabs for your `widgets', `apps' and `profile'.
In the apps tab, click `Get an AppId?'.
Once saved, click `edit' beside the new application to reveal the AppID?.
Open the Virtuoso Conductor in your browser (e.g. http://localhost:8890/conductor/, or similar). Click through the menus: Linked Data, Sponger, Extractor cartridges.
Scroll down to Wolfram|Alpha. Make sure the check-box beside the row is enabled (and push Apply), and then click the cartridge name and scroll to the bottom of the page. Copy and paste the AppID? into the API Key field.
If you have Meta-Cartridges installed and wish to use Wolfram|Alpha to enhance other sponger queries, repeat the same process in the Meta-Cartridges tab.