"Where are you working? In Japan."
Translation:Càite a bheil thu ag obair? Ann an Iapan.
Cà is just a shorter form of càite (cà bheil = càit a bheil), and you can even find càite a bheil shortened to just cà’il.
EDIT: after I myself learned a bit more about it – although cà works like just a shorter form of càite today, historically it’s actually a different word. It’s originally another form of cò or cia ‘what? which? who?’ that was generalized in the meaning where?. Originally the ancestor of cà bheil? meant literally something like what is it in which…? (hence where?) and the ancestor of càit a bheil? meant literally what is the place in which…? (hence also where…?). (cf. the point c) in DIL entry for cía: http://dil.ie/8965)
Just spelling, they are equivalent and both used. There are many words and phrases that may be written in multiple ways and the spelling will vary depending on a writer, publisher (in case of books and newspapers), or time (spelling conventions change with time).
In older texts you’ll often find things like: am bheil…? instead of a bheil…?, dè an t-ainm a tha ort (what is your name?) instead of … a th’ ort, cò a rinn e? (who did it?) instead of cò rinn e?, in vocative a Eòghainn instead Eòghainn (with silent a written before a vowel), etc.
The Duolingo course mostly sticks with newer spelling that avoids writing silent sounds, especially vowels (so th’ instead of tha when the a is not pronounced), or it requires you to drop a before nouns starting in a vowel in vocative (Anna, Eòghainn, fhir, instead of a Anna, a Eòghainn, a fhir). But in case of càite a/càit a they used the older fuller spelling (càite a) and not the newer with silent vowel omitted (càit a).
For some reason, this sentence shows càit a bheil instead of càite a bheil as the default translation, unlike the other sentences in the course… Maybe they are switching to the new spelling and this sentence got updated quicker for some reason? Anyway, both technically should be accepted as correct.