You would need to use window.opener from new window to access parent.

http://www.codeproject.com/Articles/25388/Accessing-parent-window-from-child-window-or-vice

Also check http://stackoverflow.com/questions/13311812/popup-window-accessing-parent-dom

It is precisely what I'm using and does not work for me.

In the main window I have the grid PHPGRID called materiales
In the popup window is the PHPGRID grid called resumen

What I need is to navigate through the grid of the main window
and update the data in the popup window grillla

the code I use is:

var filaresumen = 0;
for ( var i = 0; i< filas ; i++) {
var mater = jQuery('#materiales').jqGrid('getCell', i , 'COD_MATER');
window.opener.$('#resumen').jqGrid('setCell', filaresumen, 'MATER' , mater );
++filaresumen;
}

filas is the number of rows in the main window grrilla
COD_MATER is the title of the column of the grid that I want to update on the grid popup window

2 suggestions …

1) If you are using this code in popup page & materiales grid is on parent, then … window.opener will be used with materiales not resumen.

window.opener.jQuery('#materiales')……

2) In get/sellCell, you need to pass column name set in $col["name"] as 3rd argument (not title).