"How is your uncle in Tokyo?"
とうきょうのおじさんは おげんきですか。 Using the お before the 元気 (げんき) is also possible and I little more polite.
Just as a side note for any future readers: a lot of times お is put before words to make more polite/formal. For example, while じさん is a a valid way to say uncle, おじさん is more polite.
As another side note, you'll also see ご used in the same way, although less common. Which one used depends on the word.
Commonly chinese words made of multiple kanji are used withご while Japanese words with one kanji/kunyomi readings use お. But you can see it doesn't happen all the time since under these rules it would be ご元気。
as I'm writing this message, it isn't accepted without the お anymore. But I thought it isn't wrong, just impolite?
Well, the kanji for おじさん does exist, but it's usually written in kana alone.
That said, I typed what your comment said, and it marked me wrong. I've reported it.
wish they would use kanjis at least for place names. you see the other words spelt out sometimes but never places.
I wish we were at the skill level to say "tokyo ni iru ojisan" instead of "tokyo no ojisan" .. feels more precise.
And in this lesson we should be able to put it. I was searching for the ni particle and couldn't find, very frustrating to learn a language like that
Why is it Tokyo no ojisan? Is it that he belongs to Tokyo? That sounds soo weird. Shouldnt the proper particle be de?
No can be used in lots of ways including where something is from/based. An apple pie from tesco is Tesco no ringo no pai. Australian wine is oosutoraria no wain. It's just a quirk of the language.
FYI you can find the same weirdness in Chinese: 東京的叔叔 (的 being the Chinese equivalent of の) would be the natural translation of "the uncle in Tokyo".
You can see similar titles in English and other languages. For example, Helen of Troy, Sir Lancelot du Lac (of the lake), etc.
It is more "that is related to" than possession. Like you can say 東京のおすすめ (a specialty of/from Tokyo).
This literally got marked wrong just because 東京 was written in kanji... The keyboard input is almost unusable in it's current form. I understand that this is not so easy to implement, but at least add some automated conversion for hiragana/kanji usage please.