Translation:How is your aunt in Osaka?
In Japanese, you can't place two nouns in row. You have to place の in between. I got all my info from https://www.wasabi-jpn.com/japanese-grammar/particle-no-possessor-and-modifier/
It is probably because in Japanese course, Duolingo insists on us learning Japanese language in Teineigo (丁寧語), which is its standard polite form. When we talk to people we don’t know that well or they are complete strangers, we use that form of talk (it is where we use です for “to be”, verbs with −ます forms, prefixes お- and ご- and so on).
However, missing out casual Japanese in Duolingo is kind of unfortunate in my opinion, because it still plays a great role in-family and friend-to-friend speech, not to mention songs and cartoons. If you want to learn casual forms and how they work, I suggest you to find on the internet. Like, after finishing the first introduction lessons, I was really confused when I saw that it had said in one lesson “most of the verbs end in -ます”... which isn’t entirely true (it’s only the polite form, while all the verbs end in う-syllables or る syllable). Yeah, that really got me confused and frustrated. At least now I know the difference.