[Electronic M]

In electromagnetically deflected CRTs like the 10BP4 the secondary emission electrons are drawn to the internal aqua-dag coating which is connected to the HV second anode button that connects to the HV rectifier which is hooked to the flyback.

On electrostatic deflection CRTs like the 7JP4 the deflection plates have several hundred to a few thousand volts of positive potential applied to them. The negative electron beam is attracted to them and which ever plate is more positive the scanning beam will move toward(and touch if the plate is ran too positive). The secondary emission electrons are drawn to the relatively positive deflection plates and complete the beam current loop through the HV supply connected to the plates.

EDIT: (missed the last couple of posts when posting the above) The secondary emission does not need the glass to conduct it. Electrons can travel freely in a vacuum(otherwise the scanning beam could not form) so they can just take the shortest unobstructed path between the point on the screen, where they are formed by secondary emission, to the most positive element in the vicinity(the deflection plates in an electrostatic tube or the second anode in electromagnetic tube).