Suppose to do something mischievous for a job but cant figure out how to do it

You can interact with other sims and choose Mischievious interactions from there. Some of those interactions are mild pranks that can amuse the other sim without hurting them.

You can also get a Mischief skill book and study it until you can get to about level 2 or 3, then troll people on forums through a computer. Trolling for a couple of hours is usually enough to fill the job requirement.