Could you specify the product you are using, whether it is RadGantt for ASP.NET AJAX as set in the thread's info or Kendo UI Gantt as shown in the screenshot you attached? If you are using Kendo Gantt you could export the visible part of the Timeline View using the corresponding classes (highlighted in yellow below) and kendo drawing, for example:
drawing = kendo.drawing;
".k-timeline > .k-grid-content"
Alternatively, if you are using RadGantt for ASP.NET AJAX, the ClientExportManager
is the control that can export specific elements on the page.