For a report I found this suggestion from a PM on the idea posted here...
For internal license usage, edit a report type based on Users and in
the page layout, add a field lookup following this path:
User=>Profile=>User License; from there you have access to "Total
Licenses" and "User License ID". In your report add a filter on the
user license ID and it will return all the users in this license.
Update based on comment: From the help here they suggest doing an export and point to another idea here.
As there is currently no option to create a report on a list of
Service Cloud Users.
The current work around is to use the Apex Data Loader to export a
list of users (with) or (with and without) the "Service Cloud User"
The field on the user object which holds the "Service Cloud User"
checkbox value is "USERPERMISSIONSSUPPORTUSER". Using the data loader,
we can export a list of users with service cloud user checkbox enabled
by adding a filter USERPERMISSIONSSUPPORTUSER=TRUE
This Column / Field does not show up when you are using the Data
Export Services. So Apex Data Loader is the only workaround as of
Vote for the current Idea in the Idea Exchange if you would like for
this to be reviewed and possibly implemented by clicking the link
You can query for this field as well, tested in the developer console
Select USERPERMISSIONSSUPPORTUSER from user