What is QZHQSSRV job?

On the as400, QZHQSSRV is one of the prestart jobs that will be running in the QUSRWRK subsystem.

A prestart job is a batch job and will run on the server before a program on a remote system tries to connect with that server. Usually multiple prestart jobs of a particular type are configured to run. Prestart jobs are run to increase performance of initiations and connections to a server. Host server functions, that use prestart job, use the sockets communications interface support

The host servers are:

Network print server
Remote command and distributed program call server
Central server
Database server
Secure database server
File server
Secure file server
Data queue server
Signon server

These are the programs called when the prestart job is started for host server.

Network Print QSYS/QNPSERVS
Remote command and program call QSYS/QZRCSRVS
Central QSYS/QZSCSRVS
Database QSYS/QZDASOINIT
Secure Database QSYS/QZDASSINIT
File QSYS/QPWFSERVSO
Secure File QSYS/QPWFSERVSS
Data Queue QSYS/QZHQSSRV
Signon QSYS/QZSOSIGN

The prestart jobs usually take the name of the program that they call, so QZHQSSRV is a prestart job for a remote system to communicate with a data queue on the server.