Research the GTRR (go to related record) script step. It's purpose is to take you (via new window, likely) to the exact related record(s) you are ON (where the button is clicked). The layout called would be one that shows the line-item context (the child not the parent). If you need to print ALL the instructions for this order, they would be shown (as GTRR goes to all related records). If you need just the ONE row item, then you pass a variable that allows you to find (in another window) by whatever is unique (primary key, perhaps?) to that related record in the layout showing the context of the child.
(and follow the links on the page)