Apple claim you can reveal the Notification Center with a simple two finger swipe from right to left on the trackpad, but what they don’t mention is the swipe has to start from the very edge or off the right of the trackpad for it to register. Otherwise the standard two finger scroll will kick in.

If you use a Magic Mouse you’re left gesture-less, but you’re able to add Notification Center as a hot corner. The top right of the screen makes the most sense for this as that’s where the Notification Center icon is.