As far as I know there are no standard way of doing this, it seems that the way the objektkatalog is implemented is specific to GeoNorge and you'll have to look around in their API to see if they have some sort of discovery service that lets you list all the available package IDs.

An alternative would be to contact technical support at GeoNorge to see if they can help with the relevant information.

Try plaing around with this URL, as long as you specify "text=<something>" it returns a CSV containing a list of all the matching objects with their ID, here's an example looking for "FKB", you'll find your example object in the result:

https://objektkatalog.geonorge.no/api/search?text=fkb&navPaths=&limit=5000&mediatype=csv

It doesn't seem to work if text is left blank, you you have to have an idea for what to look.