Ian White gives the following diagram to explain what goes on at the coax to dipole junction.
He labels five currents in his explanation.
Let’s simplify that
Above is a diagram from Common mode current and coaxial feed lines showing the currents where a coax connects two two wires.
Lets morph that to the dipole feedpoint topology.
The whole thing is defined by just two currents, I1 and I2. The common mode current Ic=I1-I2. There is common mode current present in the short two wire connection to the dipole, and on the outer surface of the coaxial cable.
Note that I1, I2 and Ic are usually standing waves (ie they vary with location), and so these currents are defined here at the point where the conductors meet the end of the coax.
Are the currents measurable?
Using a clamp on RF current probe, the currents on the each of the two dipole conductors I1 and I2 is measurable, and so also the current on the outside surface of the coax shield Ic.
Remember also that these are sinusoidal AC currents, and I1, I2 and Ic refer to the magnitude of the currents.
The three currents can be resolved into the common mode and differential components, see Resolve measurement of I1, I2 and I12 into Ic and Id
(I12=Ic, the current measured with the probe around both two wire conductors or around the outside of the coax.
Can the currents be measured at an elevated dipole feed point?
Sure. I have done measurements of Ic over the length of coax by hoisting a current probe on a separate halyard to raise and lower it and reading it from the ground with a spotting scope.
Recall that Ic is usually a standing wave, and when you measure it at just one point, you don’t know much about it.