Could you build your query over process assignment and set the criteria to be where Class Type = Assignment (you'll need to ensure you select the correct Assignment for incident as when you drop the list down you'll see Assignment relating to Incident, Change etc). The second criteria could be where Process Assignment Serial Number = 1 (so you get the first). You could then add Group as a prompt user parameter
This will only work if the 'initial' assignment you need is the actual first assignment incidents go through e.g. here all incidents get logged to the service desk on creation (when logged via email) so the 'initial' group assignmnet we're interested in is actually the one that the sevrice desk assign to. Whereas if an analyst logs an incident manually then the group the incident is assigned to is the analyst current group and therefore this is the 'initial' assignment that is relevant.
Hope this makes sense and helps
Thats great thank you works perfect!