There is a report under System admiration > Reports > Licensing > Named User License Counts. This report contains information about the users who are assigned to security roles in Microsoft Dynamics AX. The report analyzes the roles and privileges that are assigned to each user and then calculates the number of licenses that are required for each user type.
To actually get data to show up on this report you have to set up a batch job to run periodically. Its a little hidden.
You can copy and paste the job below. Then run it to create the batch job. This sets up a batch job to run once a week. Which seems a bit much. I think once a month on a weekend is sufficient.
static void LicenseMinerCreateBatchJob(Args _args)
Alternatively set up a batch job to run SysUserLicenseMiner class.
Some good info on licensing.