Which storage system command would display the WWPNs of hosts that have logged into storage...

https://library.netapp.com/ecmdocs/ECMP1196979/html/man1/na_fcp.1.html

fcp show initiator [ -v ] [ adapter ]

If no adapter name is given, information about all initiators connected to all adapters are shown.

The command displays the portname of initiators that are currently logged in with the Fibre Channel target adapters. If the portname is in an initiator group setup through the igroup command, then the group name is also displayed. Similarly, all aliases set with the fcp wwpn-alias command for the portname are displayed as well.

If the -v flag is given, the command displays the Fibre Channel host address and the nodename/portname of the initiators as well.