Marker out of gpx file: display <Name> label

I have a Leaflet map which displays a bunch of locations from a .gpx file and shows them on OpenSeaMap Karte: https://www.swiftease.de/download/WP_Orte.html
Unfortunately, all OnClick-Labels are empty.

Wich code must be added to the script, in order to display “name” and/or “desc” content in label?