Add some stuff to your cart and navigate to the checkout page where you would like to add text to. Copy a phrase or wording that is significant to that page only.
Now go to Admin > Tools > Developers Tool Kit and paste the copied wording into the relevant search facility. I use the "Look-up in all files" found right at the bottom. Now select "All Files - Catalogue/Admin" in the drop down menu in "All Files Look-ups:"
Click the "search" button and you will see all files on your installation that contain the unique phrase you copied and pasted above.
Open the file(s) in your editor and add the desired text. Make sure you have a backup of the page(s) before you make any changes.
Frank
https://www.frnt.org/zencart
NOTE: We are sorry that Frank is no longer with us.
We are grateful for all his contributions to the Zen Cart community.