/usr/share/zoneinfo/

The set command is used to display or modify the shell variables and functions in the current shell. When used without any arguments, it prints the names and values of all shell variables, including environment variables and user-defined variables, in alphabetical order. The output also includes the shell options and the positional parameters. The set command can be used in any POSIX-compliant shell, such as bash, zsh, ksh, etc123.
The other options are not correct because:
* env is used to print or modify the environment variables, not the shell variables. It does not show the user-defined variables or the shell options. It can also be used to run a command in a modified environment45.
* env -a is an invalid option for the env command. The -a option is not supported by the env command in any standard or common implementation45.
* echo $ENV is used to print the value of the environment variable ENV, not the list of all shell variables.
The ENV variable is usually set to the name of a file that contains commands or aliases to be executed by the shell. It is mainly used by the ksh and some versions of bash .
References: 1: How can I list all shell variables? - Unix & Linux Stack Exchange 2: 2.1 Command Line Basics
- Linux Professional Institute Certification ... 3: set - The Open Group Base Specifications Issue 7, 2018 edition 4: How to set and list environment variables on Linux 5: env - The Open Group Base Specifications Issue 7, 2018 edition : What is the difference between .bash_profile and .bashrc? - Unix & Linux Stack Exchange : ENV - The Open Group Base Specifications Issue 7, 2018 edition

hwclock, /sbin/hwclock, /usr/sbin/hwclock
Explanation:
The command that is used to sync the hardware clock to the system clock is:
hwclock --systohc
This command copies the current system time to the hardware clock, which runs even when the system is shut down. It is equivalent to the command hwclock -w12. The hardware clock is also called the BIOS clock or the RTC (Real Time Clock)3.

The lsof command, meaning list open files, is a command-line utility in the Linux system to display information about files that are opened by processes1. The lsof command can take various options and arguments to filter and format the output. One of the options that can be used to identify the PID of a process which opened a TCP port is the -i option, which selects the listing of files whose Internet address matches the specified address. The address can be specified as a port number, a host name, or a combination of both. For example, to list the processes that are listening on TCP port 80, one can run:
lsof -i TCP:80
The output shows the command name, the PID, the user name, the file descriptor, the type, the device, the size/off, the node, and the name for each process. The name column shows the local and remote addresses and port numbers for the TCP connection. For example, the output may look like:
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME httpd 1234 root 4u IPv4 12345 0t0 TCP *:80 (LISTEN) httpd 2345 www-data 4u IPv4 12345 0t0 TCP *:80 (LISTEN) httpd 3456 www-data 4u IPv4 23456 0t0 TCP 192.168.1.10:80->192.168.1.20:1234 (ESTABLISHED) This shows that the httpd command, which is the Apache web server, is listening on TCP port 80 with the PID 1234 and 2345, and has an established connection with the remote address 192.168.1.20 and port 1234 with the PID 3456. To kill the process by PID, one can use the kill command with the -SIGTERM option, which sends a termination signal to the process. For example, to kill the process with the PID 3456, one can run:
kill -SIGTERM 3456
The other options are not correct because:
ptrace: This is not a command, but a system call that allows a process to trace and control the execution of another process. It is used by debuggers and other tools that need to monitor and manipulate the behavior of other processes2. It does not display the PID of a process which opened a TCP port.
strace: This is a command that traces the system calls and signals of a process. It can be used to diagnose, debug, and monitor the interaction between a process and the kernel3. It does not display the PID of a process which opened a TCP port.
debug: This is not a command, but a general term that refers to the process of finding and fixing errors in a program or system. There are various tools and methods that can be used for debugging, such as debuggers, loggers, profilers, etc4. It does not display the PID of a process which opened a TCP port.
nessus: This is a command that runs the Nessus vulnerability scanner, which is a tool that scans a network or a system for security flaws and potential attacks5. It does not display the PID of a process which opened a TCP port. Reference:
https://www.howtogeek.com/28609/how-can-i-tell-what-is-listening-on-a-tcpip-port-in-windows/
https://bing.com/search?q=identify+PID+of+process+that+opened+a+TCP+port