Quoting Jeroen,

A) if it's within your DMS, all you need is in System Center (where you can get your DMA IDs) or alternatively in the DATA section of any VIEW card:

There you can select your Elements or Serviceseon the left and see them listed on the right - worth noting that your element ID consists of DMA id and a numeric ID ID for the element: once, the DMAid in the element ID gave you the info about which DMA is in charge of monitoring the element, but since DELT features were introduced it is just the ID of the DMA where the element was created.
To check on which DataMiner your element is hosted, you need to refer to the "DataMiner" column of the above tables.

B) If you need to define services for any NMS implementation, it's worth involving a Solution Architect (sometimes a Service Application Architect) to make sure the technical and Business requirements are well "translated" in the definition of your destination system - this can be an overlooked necessity at times, but it will protect and future-proof your implementations.

HTH