Toc[] tocs = HelpPlugin.getTocManager().getTocs(Platform.getNL());
for (Toc toc : tocs) {
    ITopic[] topics = toc.getTopics();
    for (ITopic topic : topics) {
        System.out.println("label: " + topic.getLabel() + ", href: " + topic.getHref());
        // process subtopics topic.getSubtopics()
    }
}