I want to update how I can know my own kid better, sort of answering my own OP question. It turns out many of you are right that I should’ve known my own kid better if I paid more attention.
The school year is ending and my kid is bringing home his year long school work that I usually pay no attention to. Sifting through it I now see what types of questions he missed in a course over the year. I do wish however the school keeps track of his yearly progress over the years, not just the final grades, for later use by careless parents like me.