Hi All,
i found a solution for this problem. I know how many rows my nested grid has (count them in the datastore for the parent grid)
$("#yourgrid").on('cellclick', function (event) {
var datafield = event.args.datafield;
var datarow = $("#yourgrid").jqxGrid('getrowdata', event.args.rowindex);
var rowHeight = 43+datarow[16]*32; //<-calc your height, in my case the cnt of the rows is in column 16, an i added 43px for the header
$("#yourgrid").jqxGrid('rowdetailstemplate').rowdetailsheight = rowHeight;
});
br
chris