Translation:Which way is the exit?
for reference these are the same on practice as far as I know, どちら is just the politer way to say どこ, used in formal situations, this is related to keigo or polite speech in japanese. I don't know why everyone is posting that they are diferent though. Something similar happens to でも and しかし.
出口はどこ？ it's a perfectly fine translation for this one as well.
from my understanding, the difficult thing about a sentence like this is that どちら doesn't only mean "which way"; it's also a more polite way of saying どっち, which means "which one [out of two options]." though the fact that this is the "directions" module means it's safe to assume that "which way" is the best translation, duolingo really should accept "which one is the exit?" as well, since there's nothing incorrect about that translation of どちら without more context.
Is there really that big a difference between "Which way TO the exit?" and "Which way IS the exit?" The "to" sounds way more natural to me and I don't think the grammar of the original Japanese sentence really counters it. I guess because Duolingo tends to translate です as "is" it would make sense but... I don't know, it seems too strict to me?