To enable slow query logging, add 'logslow' => 1 to the 'dboptions' array in config.php. This will cause queries over 1 second (the '1' can be changed to any number of seconds) to be logged in the 'log_queries' table in the database.
Example
$CFG->dboptions = array ( 'dbpersist' => 0, 'dbport' => '', 'dbsocket' => '', 'logslow' => 1 ;
The 'log_queries' table can be exported and sent to Totara Support.
Most database administrations tools e.g. MySQL Workbench, PHPMyAdmin, etc., have a graphical user interface for this. You can also do this from the command line on the server.
Only enable slow query logging long enough to test slow queries and immediately disable after testing.