Electro-magnetic variations have been observed after earthquakes, but despite decades of work, there is no convincing evidence of electro-magnetic precursors to earthquakes.
No. There is no evidence of a correlation between mass extinctions and magnetic pole reversals.
At most places on the Earth's surface, the compass doesn't point exactly toward geographic north.
Not directly. High-altitude pilots and astronauts can experience higher levels of radiation during magnetic storms, but the hazard is due to the radiation, not the magnetic field itself.