Translation:At which station should I get off the subway if I want to go to the airport?
If I'm not mistaken, mít-plus-infinitive has also been translated elsewhere in the course as "supposed to."
In English, all three options are used to ask this particular question:
-- Where SHOULD I get off -- Where DO I HAVE TO get off -- Where an I SUPPOSED TO get off.
I don't have a sense of which may be used more often. Although, reading VladaFu's comments, I'd suggest that "have to" is probably less close to the Czech original than the other two... Just my two cents.