Books to prepare before reading Knuth's The Art Of Computer Programming (TAOCP)
Don Knuth is a teacher, and is always very thorough when he writes.  So one should
expect that he states all prerequisites in his books.

To ascertain that, I went to look in my own issue of the first volume.

Indeed the preface states some prerequisites on page v, which he sums
up into "the single requirement that the reader should have already
written and tested at least, say, four programs for at least one
computer".

Starting page viii, he gives a few words regarding mathematical
content.
"the material has been organized so that persons with no more than a
knowledge of high school algebra may read it, skimming briefly over
the more mathematical portions; yet a reader who is mathematically
inclined will learn interesting mathematical techniques [...]". He
calls his organization a dual level of presentation.

Later he confirms that "a knowledge of elementary calculus will
suffice for most of the mathematics in these books, since most of the
other theory that is needed is developed herein ..."

Hence my best advice is to find out what you need by first reading the
prefaces of the various volumes of TAOCP in the library.  I suggest
adding some lighter reading, such as comics.  You may need it.

A word of warning though. Knuth tends to be too optimistic regarding the brains of other people.