You need to refer to the GDL Reference Manual... and should be warned, that you would have to change the script for every door in your project, saving it out with a new name, perhaps in your embedded library... and that if a library update is posted, you would have to repeat your work on the updated library to get the bug fixes or new features.
So... I recommend that you only pursue this is it is absolutely necessary / no other way to achieve what you need. (For example - do you need the ID twice because your schedule is so wide? How about making two schedules and layout them out side by side.)
The user ID field that you see in the Info Box / settings dialog is known within GDL as GLOB_ID. Page 266, GDL Ref Manual (via Help menu), or:
http://helpcenter.graphisoft.com/guides/gdl-reference-guide/miscellaneous/
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