From Xojo Documentation

Read-Only Property (As String )
StringValue = aPopupMenu.DataField

Supported for all project types and targets.

The name of a Field in the table referenced by the DataSource property.


Relevant only if the PopupMenu is used in conjunction with a DataControl to display the contents of a field in a database table.


The following specifies the DataSource and DataField for the control. You can also set these properties in the Properties pane

Me.DataSource = "Movies"
Me.DataField = "Title"