Answer:
All of them. They all came true, and do so every generation. Often times, every year.
That's because his predictions were so vague, so couched in nebulous terms, that they can mean anything to any body. And have. And do.
He predicted a conqueror. And 200 years ago this was "known" to be Napoleon. 100 years ago it was Bismarck. 75 years ago it was Hitler. Sadly, even small time dictator Saddam Hussein got roped in and was said to have been "predicted" by the all seeing Nostradamus.
To hear his followers, I'm just a cynic, and the "Quatrains" as they are called clearly point to whoever they say. And do so in meticulous and undebatable detail. However, these same people cannot explain why if the predictions are so clear and obvious, why no one ever mentions them in advance.
Such as the supposed predicting of 9/11. If that prediction was as clear as the followers of Nostradamus claim, then one wonders why one of them didn't go there that day, pull the fire alarm that morning, and thus save several thousand lives.
As you have gathered from the above, the real answer is that none of his predictions have ever come true.