If an effect would put one 1/1 creature token onto the battlefield, and I control two Doubling Seasons, how many tokens would be put into play? 3 or 4?
Four tokens will enter the battlefield. This is actually spelled out in a Ruling on Doubling Season:
For reference, the token ability says:
This is a replacement effect, so rather than merely responding to the effect that places a 1/1 creature token onto the battlefield (and adding one more), it completely replaces that effect with a new one that places twice as many tokens onto the battlefield. So it works out like this: