As of right now, there is no way within Ninox to link two databases in different workspaces. You can use a middleware product (i.e. Make or Zapier).

You might be able to when the new version of Modularity comes out in the fall. There is talk about being able to "publish" your modules across workspaces.

• Publish – not available

  Later versions may let you package the module (including its interface) and release it to a channel so any workspace can discover and add it. During the beta, sharing is limited to private workspaces or imports (direct copies).

Don't know if this will be available in the fall or in later versions.