Which object stores segmentation data

Peter,

What do you mean by this? Do you mean any field that could be segmented by?

Or do you mean Member of Segment? The Member of Segment is based on other criteria and the lead is then made a Member. I see that once this is done, the lead shows a field called "Language Segment" (for example). So I suspect you could make a reference to it in the API. Keep in mind that it references the Segmentation Name "Segment" = Segment Name.

BUT since Segment is derived from other fields and can be changed if that underlying data changes, you might not be able to do more than request a list of leads.