>We can get the USERNAME() value in Power BI online. This is in the form of an email. That is good enough. Now, I need to create an audit trail of each report accessed. Thus, when one user accesses a report, I need to create a record in the Hit table so I have a log of what report has been accessed by who. However, DAX() functions are not usable in the query. What kind of mechanism can used to achieve such a request?

Are you referring to reports that have been deployed to your Power BI report server, or to the cloud?