How to: Display a Context Menu For Column Headers
The example below handles the ASPxClientGridView.ContextMenu event to display a context menu when a user right-clicks within the column header panel.
The image below shows the result.
<ClientSideEvents ContextMenu="function(s, e) {
if(e.objectType == 'header')
headerMenu.ShowAtPos(ASPxClientUtils.GetEventX(e.htmlEvent), ASPxClientUtils.GetEventY(e.htmlEvent));
}" />