How many times my client has joined my regular meetings

Unfortunately, there is not going to be an easy way to do this, but it can be done. You need the Usage report showing meeting attendees. You would find this information by going to Report - Usage Reports - Usage. You can only view one month at a time. 

You would need to download all the CSV files, put them in Excel, and you could create a PivotTable from this. You still have the issue that the user may use different names. For example, one meeting may by Chris Menard, the next meeting, CM, or something else. 

So, doable, but a lot of work, and not 100%. If this answers your question, please click Accept as Solution.