I open and read a data file in a conversation script to pick up dialog. The test game function works perfectly , when ran it opens the file and displays the conversation from the file.

When a standalone is created the files folder created does not contain the data files. I have tried to place the data file in the script bank, databank and other locations including the main level of folders, but it in no case is it included in the stand alone build.

The stand alone build logic does not recognize that the file that is being opened is needed in the build.

You have to tell the engine if you have files that you load your self so it knows to carry them over in the standalone, there is a special file that you add them to by I can't remember what its called.

Edited to add: The best solution is probably to create a script that writes the file for you if it doesn't already exist!

https://forum.game-guru.com/thread/220545

That worked perfectly, just be sure to place the FPP file in the same folder as the map file.

Could you not add the include line to the script that accesses it, pointing to the data file, that should tell the exporter to copy it over shouldn't it? Or does it only work with lua and audio files?

It looks like it doesn't work with files loaded via script (plane files, audio files loaded via globalsound commands, sprite image files).
For this reason, I wrote a tool than encloses all the files used over a map in one folder named the same as the map, within the entitybank folder, that way it is so easy to generate a standalone file since all the files are there, even those loaded via a script, due to my tool open/read all the scripts used over the map. There may be some vid about, somewhere.
The standalone features really needs some attention and get the focus when possible, of course.