You can call 'getEditor' method to get the current editor and then get the combo object.
onCellEdit: function(index,field,value){
	var input = $(this).datagrid('input', {index:index,field:field});
	if (input){
		if (value != undefined){
			input.val(value);
		}
		var ed = $(this).datagrid('getEditor', {index:index,field:field});
		var cc = $(ed.target);
		console.log(cc)
	}
}