There are some visual clues. First, the chip pins are labeled in the spec so you can guess they’ll be close to relevant units, and also try to trace their connections throughout the die.
Second, units like memory have an obvious regular structure because they are made from many identical micro-units
Third, if you see, for example, 16 identical adjacent units you could guess this is something that could be dealing with data 16 bits at a time. That narrows it down
There are numerous clues like those.
You could also use tricks like using a thermal camera. What part gets hot when you do certain operations?
Also, in SC5? there was a hallway that had a bunch of plaques from partner companies... and what was awesome was the amount of "Engrish"
Some of the comments were along the same line as "for great justice" (if you are aware of that old meme)
I also personally really value their work—for anyone with intermediate to advanced knowledge of electronics engineering and computers, they are an invaluable source of educational entertainment as traditional mainstream media simply doesn’t cater to such niche audiences.