Why is the article en used in this situation but not when saying "jag ar domare" (I am a judge)?
There is nothing wrong with asking vad gör domare but it actually means what do judges do i.e., plural.
Swedish doesn't use an article for personal professions and similar words. That's why you'll say jag är domare or jag är webbredaktör (web editor), but also han är socialist or hon är republikan.
For example French has very similar use of articles in these kind of cases.
Yes, and Dutch too IIRC.
And German, and Spanish, and Italian. :-)
Much thanks Emil
I have a question. Couldn't "Vad gör en domare?" be interpreted as either of "What does a judge do?" and "What makes a judge?" is there a way to tell which is the subject and which the object?
Yes, it could be interpreted both ways. And I don´t know how to tell which is the subject and which is the object except from context.