Sorry for my stupid question, but I'm not to able get a node 'gsak:Parent' from my XML file ->
<gpx>
<wpt lat="50.067" lon="14.382867">
<name>SA10ZVF</name>
<cmt>Misto k zaparkovani a startovaci pozice pro lov</cmt>
<type>Waypoint|Parking Area</type>
<extensions>
<gsak:wptExtension xmlns:gsak="http://www.gsak.net/xmlv1/3">
<gsak:Parent>GC10ZVF</gsak:Parent>
<gsak:Child_ByGSAK>false</gsak:Child_ByGSAK>
</gsak:wptExtension>
</extensions>
</wpt>
</gpx>
Thank you for your advice.