Question:  I would like to know how to change the log level for the pbs_mom.

Solution:  To change the log level on a permanent basis you would want to edit the /var/spool/torque/mom_priv/config file, adding a line like the following:

$loglevel 3

After making this change you would need to restart pbs_mom for it to take effect. 

If you would just like to change the log level for a short period of time, like when debugging a specific issue, you can do so like this:

momctl -q loglevel 7

The advantage of this is that you can make the change without having to restart the mom.  When you've captured the logs you need you can change it back the same way.