"The lawyer has a secretary."
Translation:Advokaten har en sekretær.
The key here is that there’s no reference to neither wearing clothes or having a certain profession, but to something the lawyer has (a secretary). If the sentence had been ‘The lawyer has an apple’ you also need the article. If he had had a shirt (just in possession of and not wearing it) you would need the article as well.
I've found it to be similar to English in that, if you are talking about a specific person (from all other persons), you need to say 'the'. It can't be left out when making specific references. (It's not just any lawyer being talked about, but one very specific lawyer out of all possible lawyers.) Similarly, if you're just speaking generally about someone wearing a dress, I guess you can leave out the article. (This is a new thing for me to remember.) But if you are making specific reference to one particular dress (out of all other possible dresses), then you have to include the article. E.g. Hun har en rød kjole på i dag.