Graph graphMLGraph = TinkerGraph.open();
graphMLGraph.io(IoCore.graphml()).readGraph(file.getAbsolutePath());

graphTraversalSource.E().toStream().forEach(edge -> {
      System.out.println(edge.label());
    });

<edge id="1" source="1" target="3">
<data key="edgelabel">belongs-to</data>
<data key="weight">1.0</data>
</edge>
<edge id="2" source="1" target="4">
<data key="weight">1.0</data>
<data key="edgelabel">part-of</data>
</edge>

<key attr.name="Edge Label" attr.type="string" for="edge" id="edgelabel"/>