School Zones

You can't see that file on your unit, or any other unit for that matter. It inside a file called CustomPOI.gpi or whatever poiloader made or you named it.
It's located in the POI directory in the root. If you fire up your unit you should find the the file under Where to?/Categories/Custom POIs. There you'll find all you put in there using poiloader.

I believe you are not referring to a POI file you created and installed on your Nuvi. The School zone CSV files located on this site do not include any from the New York area where you are from.

The school zones on your 3597 are embedded in the map you are using and CANNOT be accessed.

Straight from Garmin:
The school zone alert feature is a relatively new feature that has been implemented in Garmin's newest automotive models. Your device has data for most school zones in major metropolitan areas, however not every school zone may be covered. This data is built into the mapping file and is updated along with the map data when you download map updates to your device.

Source of information:
http://www.poi-factory.com/node/41301
Scroll down to charlesd45's post, it's the 10th post down.