I do not think there is any good way to make print outs of the App Inventor blocks code.
What I do is:
In Windows 7 (also works in Vista and newer version) is to use the Snipping Tool to select a section of blocks code on screen, copy the selection, and then paste that into a Word document. I make several “snips” as needed, to capture all of the code, and paste each into the document. Then I print out the document.
Is there a better way? I do not know but if you have a better solution, let us know in the comments! Thanks!