This tutorial from the British NHS demonstrates how to confirm NJ tube placement:
www.asph.mobi/Guidelines_Neonatal/Naso-Jejunal%20TUbe%20Insertion.pdf

http://www.uhs.wisc.edu/health-topics/tobacco/documents/Five_Day_Plan.pdf

Pubmed research confirms its effectiveness:

https://www.ncbi.nlm.nih.gov/pubmed/17697483