There's only one wire going to my knock sensor, but two terminals on the sensor. Am I missing something, or is this how it is supposed to be?

 

That's correct

 

There is only one wire, and a shield. The shield is connected to the ecm harness. Don't know why tje sensor has two terminals though.

 

I think it is because Nissan didn't want to buy a one wire connector. That is a common thing in the electronics world to use a bigger connector that you already have rather than buy another one and have to stock another item.