Are you using Editor.EditVertices? If so, you can subscribe to Editor.EditCompleted event.
private void Editor_EditCompleted(object sender,Editor.EditEventArgs e)
{
if (e.Action == Editor.EditAction.EditVertices)
{
foreach(var edit in e.Edits)
//TODO: use this edit.Graphic
}
}
If you are performing the geometry edit yourself, I imagine you are using some layer mouse events to get to select a graphic for editing.
private void FeatureLayer_MouseLeftButtonDown(object sender, GraphicMouseButtonEventArgs e)
{
//TODO use e.Graphic
}