"Where" is perfectly correct. Instead of "where test takers must read" you can also say: in which test takers must read... that ask test takers to read... requiring test takers to read... These three suggestions view questions as "things": "a thing in which..", "a thing that...", and "a thing requiring..." It is also permissible to think of a question as a place, and that is why it makes sense to talk about "a question where..." Here are other examples where "where" refers to things that are not places: "Adding fractions is where I met the limits of my mathematical abilities." "The piano concertos of Mozart are where I found my bliss". "He is a great dancer, but the tango is where he really shines."