Where can I find the Licence Key?
You can find the license key in the “purchase confirmation” email that you received after the purchase. It's referred as "purchase code".
You can also find it on the downloads page at Envato.
Log in to your Envato account and go to your downloads page (http://videohive.net/downloads). Locate the product you have purchased on the list and click on the “Download” button. That will open a dropdown menu listing an option to download the item or the “License Certificate and Purchase Code.”
After you have downloaded the certificate you can open it and copy the Item "Purchase Code":