One can interpret in different ways what you mean under "i need to show a subgrid on mouse hover". I suppose that you need to expend the subgrid on hovering of the rows.
I modified the demo from the answer to demonstrates one possible implementation of the requirement. The results you can see here. The implementation consists from inserting the following code inside of loadComplete
callback:
loadComplete: function () {
var $this = $(this);
$this.find(">tbody>.jqgrow")
.mouseenter(function (e) {
if ($(this).find(">td.ui-sgcollapsed").length > 0) {
$this.jqGrid("expandSubGridRow", this.id);
}
});
}