Own a 2008 FX35... want to add an EFIE along with a hydrogen fuel enhancer to increase mileage. How many oxygen sensors are there on this model and where are there? Or, where can I obtain the information?

Normally a potential automotive reengineer would download and study the Factory Service Manual before embarking on a redesign of fuel system.

Nissan and Infiniti have a $19.95 per 24 hours site with all FSM and TSB

Tampering [or redesign] with OBD2 emission control is a felony violation of the Clean Air Act.

It will surely void the engine and catalytic convertor warranty due to changes in A/F ratios.