How can I add a link to the original repository where a resource is hosted (landing page) to a CMDI record?

If you want to add a link to the original context of the metadata file, e.g. to the repository where it is hosted (example), add a ResourceProxy of the type LandingPage, e.g.:

<ResourceProxy id="lp">
    <ResourceType>LandingPage</ResourceType>
    <ResourceRef>http://hdl.handle.net/11858/00-097C-0000-0008-E130-A</ResourceRef>
</ResourceProxy>