CERT_MIGRATION is a standard SAP Structure so does not store data like a database table does. It can be used to define the fields of other actual tables or to process "Struture for USREXTID->CertMap Migration" Information within sap ABAP programs. This is done by declaring abap internal tables, work areas or database tables based on this Structure. These can then be used to store and process the required data appropriately. i.e. DATA: wa_CERT_MIGRATION TYPE CERT_MIGRATION.
The CERT_MIGRATION table consists of various fields, each holding specific information or linking keys about Struture for USREXTID->CertMap Migration data available in SAP. These include SUBJECT (Subject), SUBJECTH (Hash Value: Subject), ISSUER (Issuer), ISSUER_EXTID (Issuer from Classic Mapping)... See below for full list along with technical details, documentation, text table, check tables, foreign key relationships, conversion routines, relevant tcodes and example ABAP select code etc. .