Could someone show me which one is called by the knot vector and how to define it?
This may help:
It mentions that the knot vector is a list of numbers not a real vector so maybe its related to the point numbering.
There are a number of different definitions of "knot" in different types of mathematics. From your graph it appears that you are approximating a function by a "broken line". In this case the "knots" are the points at which the different line segments join so your "knot vector" is simply (b0, b1, b2, b3).
Separate names with a comma.