Translation:I know a girl whose father is a lawyer.
Well, then there's my approach. Some of these units do have some strange lessons. So I look at what I'm trying to get out of learning Italian, and that's to be able to travel and be conversant. So some of these questions/units I get through and move on. For example, why are future and past tense so far down in the unit structure? That's something I really wish to learn. Clitics? Not so much!!!
In British English we wouldn't say attorney, except if talking about the Attorney General. We use lawyer as a general term, and that can be split into barrister and solicitor. I don't know if those are accepted as I've only used lawyer, but maybe this is an instance of Duo using the British translation instead of the American one? Though I agree that I've heard this widely used in the States and think it should be accepted.
Sabin181036, in English you could actually use either the definite article ('the') or the indefinite article ('a'), but it depends on how the word 'lawyer' (in this example) is used in the sentence. Consider the following example: "Do you know who is representing John in his court trial?" "I know a girl whose father is the lawyer" would be a proper response because you are talking about a specific lawyer in a specific situation. But now consider this example: "Do you know anyone who is a lawyer, because I need one?" "Sure, I know a girl whose father is a lawyer." In this case, you are referring to any lawyer.