I was relieved that you guys have common sense.
I took a common knowledge test, but my results were terrible.
How about putting common sense aside and thinking outside the box for a second?
Normal discerning is the discerning you do on a daily basis, without thinking. It is all the things that you do that are common sense.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.