Where is a UI-configured Views display definition read from?
The table {views_view} has the list of views.  The more or less matches up with what is on admin/structure/views, except for views created by modules.

The table {views_display} has displays for each view, keyed to {views_view} with the vid column.  The id column is the machine name from admin/structure/views/view/foo/edit.  There is one row per display.  The display_options column has a serialized version settings from the edit form, and it more or less matches up with the display section when you export a view from admin/structure/views/view/foo/export.  I am also pretty sure that the actual query is essentially built up from the same column.

In my years of using a sledgehammer to make Drupal do what my clients need, I don't recall ever poking through the views tables for anything.  I will periodically look at an export to see what is going on with a view, and export/edit/import views to adjust things, though.