We work only with non-technical jobs like marketing, biz dev, sales, etc (we think technical jobs are quite different). And then we have two different types of challenges: 1) Challenges that individual employers create 2) General industry challenges that candidates can use to apply to lots of jobs.
In terms of how we come up with the questions, we mostly just ask employers: "What does this employee do at work" and then we ask candidates to do similar tasks.