This is an answer to a question I couldn't find, maybe it will be helpful for some.

The Node Id in DataMiner Cloud Admin can be found on the agent in the file "c:\ProgramData\Skyline Communications\DataMiner Orchestrator\Data\NodeId.txt"

We have recently migrated some agents to another machine and had to remove the old nodes from the Cloud Admin, only way to identify them was by the Node Id (as Name and DMA ID was same), which can be found at the above location.

Thanks to Baptiste Pattyn and Jan Vanhove for the pointers.