Prospect IDs in Sphere can be located in the individual record, in the Profile > Personal > Identifiers section, and also on the Profile Summary page. There are two primary IDs available for this purpose:

Supporter ID, which is system-generated, and is unique to each record.  This ID will always consist of 9 system generated numbers.

Alternate ID is user-defined.

If you wish to load an existing ID field into Sphere/P!N that is used in another database, it is recommended that the Alternate ID field be used. In existing databases where Alternate IDs already exist and need to be changed or updated, you can utilize the Supporter ID for this purpose.