Please advice,
how can I put CheckBox at TableHeaderCaption for GridEdit and by clicking that for Check/Uncheck All Column Checkboxes
Try to follow the logic that implemented by the generated code for Checkboxes control that located at the very left side of table in List Page.
To display those Checkboxes control in that List Page, you may choose “Selected records” from “PHP” → “Page Options (Global)” → “Export” → “Export type”, and then re-generate ALL the script files again.