Where is the knock sensor on the 1996 Nissan Altima?

Knock sensor

The knock sensor for a 1996 Nissan Altima is located on the backside of the block above the oil filter.

But before you go and change it out, run a tank of the best/hightest rated gas you can find and see if that fixes the problem. On my 1995 the Knock sensor is located under the plenum and intake manifold on top of the middle of the block.