RadGanttView doesn't support exporting of its text view. However, you can use the RadGanttView.Items collection to build a flat data collection. Then, you can use the RadGridView's export functionality. Bind the grid to the self reference collection and export it by using the GridViewSpreadExport. I have prepared a sample project for your reference. Note that this is just a sample approach and it may not cover all possible cases. Feel free to modify it in a way which suits your requirement best.
I hope this information helps. If you have any additional questions, please let me know.