I don't know much about knot theory but I know that Meike Akveld taught knot theory at both high school and university level. Here's a bibliography of one of her courses at ETH Zürich:
https://www2.math.ethz.ch/education/bachelor/lectures/fs2015/math/knot/bibliography_FS2015.pdf
It includes Englisch and German books both for high school and university level. I only list English books for university level:
General books about knots - accessible to (under-)graduate students:
- M.A. Armstrong, Basic Topology, Undergraduate Texts in Mathematics, Springer-Verlag, 1983 - Chapter 10 is devoted to knots.
- G. Burde, H. Zieschang, Knots, Walter de Gruyter & Co., Berlin, 1985.
- A.Kawauchi, A Survey of Knot Theory, Birkhäuser Verlag, Basel, 1996.
- W.B.R. Lickorish, An Introduction to Knot Theory, Springer-Verlag. New York, 1997.
- C. Livingston, Knotentheorie für Einsteiger, Vieweg, 1995 (also available in English).
- K. Murasugi, Knot Theory & Its Applications, Chapters 5 and 6, Birkhäuser Boston, 2008.
- J. Roberts, Knots Knotes, unpublished lecture notes, 2010, http://math.ucsd.edu/~justin/Roberts-Knotes-Jan2015.pdf.
- D. Rolfsen, Knots and Links, AMS Chelsea Publishing, 2003.
There are still old exercises and solutions from the class available online here. They usually get deleted a year or two after the class, so I'd download them just in case. Plus, you can find some hand-drawn examples on the lecture website itself.