You are analyzing this backwards.
You are correct that Trump would not know every line of a thousand page tax bill. So one question you might ask would be, "What lines would he know more about?" And then, "Why?"
Anyone who has any insights into Trump's personal history and locale would then say, "Ahhh, maybe I get it."
This is not terribly opaque, but it takes a little grasp of the president's gestalt and owes-ies.
Anyway, that's enough. If the response is, "He doesn't read every line of a thousand-page bill," well, no kidding, Sherlock.
Sometimes I wonder how you guys, bright as you are, make it across the street without a signal. I mean, holy fuck, some of you think the world began with your birth.