Fails emissions for nox it was 2100?

Have the exhaust gas recirculating valve check out-its purposes it to reduce nitrogen oxides-Nox

Also, a worn out catalytic converter can cause high nox as well. FYI, this guide may be able to help as well.

https://www.2carpros.com/articles/smog-test-inspection-information

Here is the location of the cat so you can have it checked out. Check out the images (below). Let us know how it goes