"Knocs electrons off" is in this sense quite a simplistic way to describe it. Rather see it like this:
- The photoelectric effect is when a photon (light) excites an electron. "Excites" means that it has enough energy to move now (it is in the socalled conduction band). Moving electrons is current.
Just remember that this material from which the electrons are "ripped off" from - or rather excited in - is a part of a circuit. In an electric circuit the electrons moving away are as part of the current replaced by new electrons right away from further down the circuit.
Electrons are moving around the circuit at all points at all times if you have a steady current.