"Where is the bank's exit?"
Definition of どちら at jisho.org:
which way; which direction; where
which one (esp. of two alternatives)
From a native Japanese speaker at HiNative:
doko is like an English word of ”where”.
On the other hand, dochira has also meaning of ”where”, and it has ”which” too.
Where is Osaka station?
Which do you like, rice or bread?
From Rocket Languages:
Here's a little lesson on DOKO and DOCHI::idea: Doko asks "Where~?" while Dochi, the short version of Dochira, means "Which~?" So, " -- wa doko desuka?" "Where is -- ?" " -- wa dochira desuka?" "Which way is -- ?" However, the tricky thing is, dochira desuka? is also a formal version of doko desu ka? both having the SAME meaning "Where is ~" :shock:
My dictionary (Berlitz) translates どちら as 'which one' not 'where'. Would it be better to make the English sentence 'which one is the bank's exit?'if this is the 'correct' Japanese translation? The previous examples use どこ for where - which is not offered in this selection. This is confusing.
that's not how は and が works
「銀行の出口」it's just a topic, and you are asking something about it「どちらですか？」
And since you are making a question about this particular thing, using は makes more sense, because you are stressing the 出口 from the bank and no other things, it's like saying "speaking of the exit of the bank, where is it?".
If you use が the ～が puts too much emphasis on the「銀行の出口」and you end up with an awkward sentence that sounds rough, I'm actually not sure if the question would make sense, but it would probably be used if the context allows it.
Since the speaker of the sentence is asking the listener where is the exit, the speaker is assuming that the listener knows what "the bank" is and what the "exit of the bank" is (at least conceptually). This is shared knowledge between them, and the topic is always understood between both the speaker and the listener, but if you use が is like you are telling him new information or choosing between a list of places and asking about it at the same time, which is exactly the opposite of what you think it does...