Specify default filter in jqgrid

I suppose that you use advanced searching for the filtering. The filter is nothing more as the value of postData.filters. See here and the demo from another old answer for details.

Moreover I would recommend you to read the demo where I describe how to use localStorage to save some user preferences of the grid inclusive the searching filter. Moreover I describe why I think the usage of the localStorage the better way as the usage of cookies or session variables.