> eventually only read vol 2 because I was interested in (pseudo) random number at that time

Your comment comes at the perfect time, I am looking at learning about random number functions and tests of randomness myself. Do you have any other resources about these topics?

Some statistics books, perhaps? I think there are some references on them. I don't study random numbers anymore because my interest changed few years ago.

How long did it take you to read these 3 books and did you read them in depth?

I never finished them, mainly because I treated them as references, e.g for in-depth mathematical analysis :D

Say for studying data structures, I'd recommend a general text book like Weiss or Sedgewick. It's very rare I study Knuth directly.