In RACF, to list all the Realms, it can be used the command RLIST REALM * ALL.
What is the Top Secret equivalent to this?
The Top Secret equivalent to RACF's RLIST REALM * ALL is TSS LIST(SDT) RACREALM(ALL)
To list ACIDs with access to a REALM, the command is
TSS WHOHAS RACREALM(<resource>)