The httpd command line tool with the -v flag can be used to display the version of IHS that is currently installed.

~]# /opt/IHS/bin/httpd -v
Server version: IBM_HTTP_Server/9.0.0.10 (Unix)
Server built:   Sep 24 2018 02:53:17

Or the apachectl command line tool with the -v flag can be used.

~]# /opt/IHS/bin/apachectl -v
Server version: IBM_HTTP_Server/9.0.0.10 (Unix)
Server built:   Sep 24 2018 02:53:17

Or you can simply view the content of the version.signature file.

~]$ cat /opt/IHS/version.signature   
IBM HTTP Server 9.0.0.10

Be aware that if you installed an interim fix, the output will include the interim fix (PH51982 in this example).

~]# /opt/IHS/bin/httpd -v
Server version: IBM_HTTP_Server/9.0.5.14-PH51982 (Unix)
Server built:   Jan 26 2023 11:53:45

~]# /opt/IHS/bin/apachectl -v
Server version: IBM_HTTP_Server/9.0.5.14-PH51982 (Unix)
Server built:   Jan 26 2023 11:53:45

~]$ cat /opt/IHS/version.signature   
IBM HTTP Server 9.0.5.14-PH51982