public IReadOnlyList<NetworkDiagram> GetNetworkDiagrams()

public void GetNetworkDiagramFromDiagramTemplates(UtilityNetwork utilityNetwork)
{
  using (DiagramManager diagramManager = utilityNetwork.GetDiagramManager())
  {
    // get the first templates
    DiagramTemplate template = diagramManager.GetDiagramTemplates().FirstOrDefault();

    // get the network diagrams fromt he template
    IEnumerable<NetworkDiagram> diagrams = template.GetNetworkDiagrams();

    // or get a network diagram by name
    NetworkDiagram diagram = template.GetNetworkDiagram(diagrameName);
  }
}