Translation:Bu cami iki bin on birde yapıldı.
First, you can't use numbers on Duo. Second, since you give a specific year it's probably the most important info here so it should come just before the verb.
İki bin on birde bu cami yapıldı. is also correct but has a different emphasis. You can report it though.
Yes it can be but it implies that you didn't witness it and you heard it later.
I don't know if this would have worked weeks ago, but I was able to give "bu cami 2011'de yapıldı" as a correct solution. So you can use numbers on Duo.
sometimes they may provide numbers as a correct solutions too, but in general it's much safer to write them as words.
And what's the point in coming here and "translating" two thousand eleven to 2011? I mean, seriously...
In Turkish, a word is emphasized if it'd the word before the verb. So, the sentence you made would emphasize that a mosque was made, when it's supposed to emphasize that it was made in 2011. Don't worry though, no one really cares about this in Turkey :D