The SpaceURI is the unique identifier that characterizes one workspace. The SpaceURI can be found in the URL of the Explorer, for instance. It looks like the following:
https://itonics-gmbh.itonics.io/explorer/UsHicSHE10EnYDSA
The ElementURI is the unique identifier of each content element in the system. When you open a content card in full-view mode, you'll find the element URI as the last alphanumeric code, e.g., https://itonics-gmbh.itonics.io/explorer/UsHicSHE10EnYDSA/detail/2lbeJR55bcqES4kq