Back
Relationship referencing and reading values of relationship attributes
When using two way, one to one relationship between collections, what would be used as reference for the value of the relationship variable. I've set the display name to a string attribute, would it be the document ID instead. In the context of user data management.
TL;DR
In a two-way, one-to-one relationship between collections, the reference for the value of the relationship variable would typically be the Document ID. This is especially true in the context of user data management. 
Do you mean what would you put in that field? Then yes, it would be the Document ID
