[NumberCruncher]

This is not the exercise you need. Stakeholders aren't machines knowing the answer to any question, even if they think they do.

Some good methods:

The technique called “Five Why’s” developed by Toyota. http://www.aaronsw.com/weblog/geremiah

Socratic questioning used by a lot of scientist: https://en.wikipedia.org/wiki/Socratic_questioning

[sabmalik]

You are absolutely right, they don't but I start with the assumption that they do and I just need to ask the right questions.