Translation:Do you know which restaurant sells soup dumplings?
I get it that the point of this is to learn what the actual dishes are, but "Do you know which restaurant sells xiaolongbao?" should be accepted. You wouldn't say "Do you know which restaurant sells bread smeared with tomato sauce and covered with cheese and various toppings?" for pizza, would you?
the 吗 goes with 你知道. If there was no 吗 it would just mean "you know which restaurant sells steamed buns"
It sounds a little strange to me to say "which restaurant sells." It might be more natural to say "has," "serves" or even "makes." Selling in that context sort of implies frozen, to-go food. Otherwise, the usage is a little strange, even though that's exactly what a restaurant does.
as of Aug 6th the given translation is 'Do you know which restaurant sells soup dumplings?' when their own lesson defines '"你知道哪家饭馆卖小笼包吗' as 'Do you know which restaurant sells steamed pork dumplings?'
I left this lesson for last after finishing the entire course because it's sooooooo bad
Not true. In fact, 包 refers to a "wrap". Since both dumplings and Chinese-style have things wrapped inside, this character is used.