Logged In users info from the Appian cloud database(MariaDB).

You could look at the login audit file and report on it. I don't believe that this kind of data is stored in the cloud db.

To view the login-audit file, access the navigation menu in Appian and select System Logs.

Is it possible to read the login-Audit.CSV form Appian application?
Is there any inbuilt function in Appian to read that file? 

You will want the Log Reader plug-in.  It's tricky to use (and a bit buggy unfortunately), but will work better than nothing.

You may want to consider using the sessionCount column from the system.csv in data-metrics.csv as well.

You may want to consider using the sessionCount column from the system.csv in data-metrics.csv as well.