Recently, I was studying knot groups and I wanted to learn some more material about them (e.g. their representations).

"Knots" by Burde and Zieschang discusses some material but it is not entirely covered. Also, Rolfsen talks about the fundamental group and Wirtinger presentation but not about the representations in the symmetric group or the dihedral group.

So, what is a good reference for knot groups, their subgroups and their representations (and related topics to the knot groups)?

entirely, as the subject is a little too thick for a not-too-huge textbook. Is there something in particular you would like to learn? $\endgroup$