Question

"which of a frequency is defined as the propagation speed divided by the frequency"

Answer 1

You record the wave, either at a point over a span of time Delta(t) or at a fixed time, taking a snapshot (a photo) over a span of space Delta(z) in the direction of propagation of the wave.. You count how many cycles of the wave you have, say N_tempo cycles over the Delta(t) or N_spatio cycles over the Delta(z)

Then:

f = N_tempo / Delta(t) (*)

or knowing the speed of the wave:

f= v* ( N_spatio / Delta(z) ) (**)

The measurement gets more accurate as N_tempo and/or N_spatio are bigger, implying larger spans of measurement, Delta(t) and/or Delta(z)

Actually, if you figured out f out of (*) then you may elect use (**) to extract, v, the wave speed