What is the command to change the password of a user?

wpasswd is not a valid or existing Linux command.

gpasswd is a real Linux command, but it is used to administer /etc/group and /etc/gshadow (group passwords and membership), not individual user passwords.

epasswd is not a valid or existing Linux command.

passwd is the standard Unix/Linux command for changing user passwords, and is defined in the POSIX standard. When run by a regular user it changes their own password, and when run by root it can change the password of any specified user account. It handles interaction with the system's password database (/etc/shadow) and enforces any configured password policies.

password is not a valid Linux command; the correct command name is passwd.