Correct me if I'm wrong, but I believe that context alters the meaning of the sentence.
On its own, the sentence means, "Is Papa already at his place?" But, let's say that I asked how my brother is doing in a previous sentence. In this case, the sentence means, like you said: "Is Papa already with him?"
Again, if I'm wrong or if anyone has more to say, please reply.
I notice that the г sound seems to vary depending on where it is. If it's at the beginning, it sounds like a G, but if it's in the middle (него) or at the end, it's more like a V. Is this correct? (This also seems to be the case for the д, which at the end of words sounds more like a T). Is there a rule our way we can remember (and help with spelling)?
There are 2 relevant pronunciation rules. One is the pairing of voiced and invoiced consonants, which results in д being pronounced as т at the end of a word. The other is the special case of г being pronounced as в in most occurrences of -его or -ого (but not all, in много, for example, it is pronounced as г).
"У" means loosely "belonging to", although it seems to usually be translated as "by" or "at". But when you say "У него есть кошка" you are saying "Belonging to him there is a cat". Which is much more naturally said in English as "He has a cat".
However, "У него", on its own, means "his place" (the location where things that belong to him are)and that's the meaning used here.
In some cases, the English translation could just be a possessive with no noun: "I'm going over to Vanya's", meaning Vanya's house, Vanya's place. Looking at the other comments, it looks like DuoLingo sometimes tries to apply that rule to this phrase and suggest "Is Dad already at his", but that is painfully wrong to a native English speaker.
I think there are some phrases where it could be unclear whether "У него" means "he owns it" versus "it is at his house". But in this case, only the "at his place" meaning makes sense -- although without context, you can't say for sure whether the "his place" is Dad's place or the place of some other male person in the story. It could be "Is that Vanya on the phone? Is Dad at his place yet?"
В references the place, У references the owner of the place.
In colloquial British English, I can invite someone to visit by saying "Come back to mine" . I could also say "Come to the house". In both instances, "my house" is what is implied, but it the former I have omitted what sort of place I live in, and in the latter I haven't confirmed that I live there.
Russian uses different prepositions for these two constructions.
I just had "Dad is already at his place" marked wrong and will report it. Correct me if I'm wrong but i was under the impression that the difference between question and statement for a sentence like this depends on inflection, which i find the duo speakers terrible at conveying.
Just had "Dad is already at his place" marked wrong. Correct me if I'm wrong but I was under the impression that the difference between imperative and interrogative in Russian is inflection, which I find the Duo speakers notoriously bad at conveying. Everything sounds like a statement.