If you are asking on how many licenses for Kentico CMS you need, than you need one license - in case there will be one web site.
It also depends on type of the license. If you will buy one web site license, you can use it for one web site only. But if you will buy a server license, you can use it for multiple sites within one physical server (web server).
And also, you need to have a license for the SQL server ;-)
For more information about licensing, please see our web site