Not sure why it is so hard for someone to give a straight answer here, but I hope this helps:

1. Open the Form 1040NR (the return must be open before proceeding to step 2)
2. In the "Ask Proseries or Search Help" search window, type in "tax treaty articles by country" and click search.
3. This search should return a link to a document titled: TAX TREATY ARTICLES BY COUNTRY
4. In this document, you will find the exact data (article number) that you need to enter.
5. I suggest that you also print this document for future reference.