There is no straightforward way to get the position of the GanttPresenterSplitter, however, you could, for example, get the Width of the Grid area of the GanttView, and more specifically the width of the visible area. It is presented by a ScrollBar element, so you could subscribe to its SizeChanged event to handle when the Grid area is resized.
I have prepared a sample example to demonstrate the approach, please download the attachment and give it a try.
Do you need help with upgrading your AJAX, WPF or WinForms project? Check the Telerik API Analyzer
and share your thoughts.