Hi Maduranga,
Thank you for using Syncfusion products.
We can add buttons in the header of child window using HeaderTemplate property. We have prepared a sample and tried to meet your requirement. In the sample, we have created a data template with button and set it as header template of child window using HeaderTemplate attached property. You can download the sample from the following link:
Sample:
Docking_HeaderTemplatePlease let us know if you need further assistance on this.
Regards,
Jessie