-- What can you tell me about Johnson's progress? Is his professionalism growing?
-- How can I say anything about him? On the very second day of his employment, you moved him to the sales department and I have never seen him since that time. His progress is out of the scope of my reference.
Is "out of the scope of my reference" idiomatic?
You could also say
John has been operating outside my bailiwick.
Your bailiwick is the "area" (e.g. sphere of activity or operations) for which you have responsibility.
John hasn't really been on my turf since you reassigned him early on.
Your turf is an informal name for the "place" (broadly construed) you're responsible for, the one you feel possessive about, the one over which you'd assert your prerogatives, such as a department in an organization, a neighborhood, a sales region, etc.
You could also say
John has been outside my purview.
Your purview is your scope of responsibility.
I'd totally understand "Out of the scope of my reference", but I don't think I've ever heard it before. It comes across as a little awkward, but pretty much fine IMO.
Your title says "not your field to comment on" and in that case I would normally use "not my field of expertise", but that clearly isn't what you want in the example.
I think instead you just want to convey that you shouldn't be expected to know anything about his progress. In which case you could use:
How can I say anything about him? On the very second day of his employment, you moved him to the sales department and I have never seen him since that time. I wouldn't know anything about his progress.
