I have asked this question in the past and was informed by support that its not possible. This seems like a pretty basic and valuable report but unless its been added to one of the recent releases I don't think its possible.
This sounds like a good feature request if it can't be done currently.
Client reporting does have its own open feature request that you can vote on here: Reporting on Clients.
What is disappointing is back when 12.2 was released and they added asset reporting they stated and I quote "With the new engine we get a more feature rich, performance optimized reporting infrastructure which gives us the long term flexibility to create new reports quicker going forward" quote taken from this post: https://thwack.solarwinds.com/community/solarwinds-community/product-blog/blog/2014/07/31/web-help-desk-looking-behind-t… That was back in summer of 2014. They have so far added 0 new or notably updated reporting features since.
Voted on this. I really hope they start taking a look at new features that people really want. The last couple releases left me scratching my head wondering where most of it came from. Unfortunately its falling behind on what the business is starting to ask for.
You can do reports on locations/departments/companies and many other fields, but Clients is not one of the fields available in the Reports.
You can, however, extract the information you're looking for by doing a SQL query directly against the database.
this thread talks about it: https://thwack.solarwinds.com/ideas/2590#comment-254759
in that thread, someone posted an MSSQL query to pull similar data; i modified it to work for my PostgreSQL database. The SQL query is below; i've slightly modified it here to add a LIMIT (to show just top 10) and changed the number of days to 90 (but you can change that number of days to whatever you want):
select d.FIRST_NAME ||' '|| d.LAST_NAME as ClientName, count(a.job_ticket_id)
from job_ticket a inner join client d
on d.client_id = a.client_id inner join status_type e
on e.status_type_id = a.status_type_id
WHERE a.DELETED <> 1 and a.PROBLEM_TYPE_ID <> 11
and a.REPORT_DATE > (CURRENT_DATE - INTERVAL '90 days')
group by d.FIRST_NAME ||' '|| d.LAST_NAME
order by count(*) desc LIMIT 10