If the system is 8.6 or below (not 9.0) there is no way to tell from the configuration/licensing on CUCM as everything gets translated to DLUs. You will need to check what your UCSS contract is for, you can do that with either Cisco account team or your Cisco partner that sold you the licenses.
As I said in my response with 8.6 and below there is no way to tell, starting with 9.0 ELM tracks.
Even though you can run ELM and user count tool against older versions, it does not address the question as it can only report on how the system is configured not what licenses were purchased.
If you are using Call Manager 9 , then the license are installed using the ELM ( Enterprise license Manager) tool only.
From CUCM 9 and above , cisco has changed the licensing architechture , unlike previous version where you had DLU now there are no such things.
When you install or upgarde CUCM 9 , it also gives you the option to install ELM as well. Licenses can only be installed upgraded or migrated through ELM tool . You cannot do it via CUCM anymore.
To access the ELM ( if installed with CUCM) just enter the ip address of your cucm and you should get an option to select CUCM or ELM.
I have 8.5 version of CUCM, so I can not use the tool ELM, the only way is to review the purchase orders that were previously