Hang around with the parents of your child's classmates. You always run into them, and they live near you. Smalltalk naturally tends towards what everyone does for a living.
Of course this knowledge is not hard to get. You just need to do their job 8 hours a day for half a year or so ... or you could have a quick chat where they get to vent about their job and you learn something new. (You don't even need to have kids for that to work.)