At level 43 Nidorino learns Poison Jab, and at level 43 Nidoking learns Earthpower, and those are both moves the other form doesn't learn. So if I evolve Nidorino at level 43, will he learn that move when he evolves or will I need a move reminder? (This is HeartGold)
Nidoking can learn Poison Jab with TM84 IN HGSS, It is obtained in the Fuschia City Gym. I suggest that you evolve Nidorino with a Moonstone before level 43, so your Nidorino (Nidoking) can learn Earth Power and then you can use the TM84 to give it Poison Jab, simple, no Move Reminder needed!
Source: The Pokemon DB's PokeDex