If it is not too late ....
Full documentation about how to use ERQL, syntax, examples is in the Power studio part of the documentation in HOPEX V2 I use today.
Maybe at the same place for V5 ?
The key to understanding the search tool in HOPEX is really to understand the meta model.
The search syntax is straight forward: Select Meta Class where Condition
The condition is then either relating to an Attribute or to a Meta Association (or a string of Meta Associations !).
Select [Org-Unit] where [Designed Organizational Process] = &name
Strings of meta associations can be connected using the . (dot)
Select [Organizational Process] where [Person Assignment].[Business Role]="Organizational Process Owner"
When using abstract metaclass use : to build the relation
Select [Organizational Process] where [System Used].[System Specification]:[Application]
I've probably spent few hours on ERQL and I can't say I've much better at it than I started.
ON the other hand - I never read a single line of documentation on servicenow filitering/querying syntax and I was able to use it from day 1.
For example, this simple HOPEX query stumped me.
List applications where "Name of Person" is "Financial Controler" .
The ERQL wizard is a nice concept - but it didn't help me. It did not have "Responsibility" or "Financial Controler" role.
Finally - plain old list of applications "Menu >> Applicaions" which shows a list of all applictions - can be filtered easilty - which is nice. But, out-of-box setup doesn't display any of the responsibility columns nor can they be added by hand through V5 web GUI (probably can with Stuidio?) .
Hopefully you found the documenation more helpful and ERQL learning easier.