In a variable set I see a reference qualifier. It's an advanced qualifier made in javascript. I searched in client scripts and various script includes, but I am unable to find that piece of code. Of course I have the name and the name of the variable Set it appears it.
What are my options?
In a reference_qual field you can execute javascript code by starting the value with:
javascript: <SCRIPT>
It is usually use to call a function which retrieves the filter or the sys_ids that the field or variable will apply, for example:
javascript: myFunction()
Those functions are executed on the server side, so in a well-design implementation they should be stored in a script include. Some legacy code could call a Business Rule declare for the Global table, so you should take a look also there (you can filter by those script includes / business rules which the field "script" contains "myFunction()").
If you paste the reference_qual content it will be easier to understand what it does.