Hello,
For mail sent to
[email protected],
[email protected] and
[email protected] @Shood is correct but for all other notifications namely those at WHM>>Server Contacts>>Contact Manager -> Notifications You can enter multiple email addresses at WHM>>Server Configuration>>Basic WebHostManager Setup under Contact information (this is where the notifications retrieve the email address/es to send to). You'll just need to comma separate them.
Keep in mind this is for server wide changes, If you want to change the contact preferences for a specific account you'll need to do so in that account at cPanel>>Preferences>>Contact Information where you can add 2 email addresses.
Thanks!