Smart city initiatives depend on robust data management to ensure the efficient use of digital resources. Managing data in these projects, especially during the development and operation of Urban Digital Twins (UDTs), is a complex task. While metadata catalogs provide a foundation for interoperability and data integration, their potential to enable knowledge transfer and reuse within and across municipalities in the UDT context has not yet been sufficiently explored. Through the formulation and empirical evaluation of four hypotheses on design principles for a specialised metadata catalog, this paper investigates how knowledge transfer and reuse in UDT environments can be supported by such a catalog. The study combines literature analysis with qualitative insights from two real-world case studies. The results confirm that a comprehensive metadata schema adapted to the components of UDTs, the use of FAIR-compliant open standards, multi-stakeholder access mechanisms, and knowledge graph representations of digital resources support the discoverability, reuse, and transfer of digital resources within and across organisations. The evaluation further reveals that usability and governance structures remain critical challenges that require future research.