Hi Hrvoje,
Please let us know the Syncfusion Essential Studio Version that you have used.
Please refer the below sample which illustrates hiding the column header of GridGroupingControl and let us know if you have any issues.
http://websamples.syncfusion.com/samples/Grid.Web/5.2.0.25/F68731/main.htmSorry fro the inconvenience caused.
Regards,
Sureshsekaran.