I think you can read at various levels though.

When I say I've read most of Volumes 1-3, I mean literally that, I read the text through. At that level it isn't too difficult to read, and you'll learn a lot like that.

However some bits I've studied in much greater detail, like for instance the multi-precision arithmetic algorithms which I had to implement. For that I read it multiple times, implemented the algorithms, did some of the exercises. That takes much much longer than just reading it through.

It is rather like reading a research paper which you do roughly like this, stopping after any step where you think it is no longer providing value to you.

    1. Read the title
    2. Read the abstract
    3. Read the paper through quickly.
    4. Read the paper through slowly being more critical, making notes.
    5. Read the paper through again working through the maths, implementing the algorithms, making sure you understand everything.

So I've read most of TAOCP at level 3, half a volume at level 4 and only 50 pages at level 5.

If nothing else I've loaded the index in my head!

PS the examples are notorious in TAOCP. The easy ones will take a few minutes and the hard ones are unsolved research problems!