Hi,
For SpamAssassin:
WHM > Service Configuration > Service manager and ensure SpamAssassin service is enabled.
WHM > Packages > Feature Manager to ensure SpamAssassin icon is accessible from cPanel interface
WHM > Server Configuration > Tweak Settings ensure "Enable SpamAssassin spam filter" is enabled.
From here you may enable SpamAssassin within each desired cPanel account. If you require all cPanel accounts to have SpamAssassin enabled, select "SpamAssassin™: Forced Global ON" at WHM >Service Configuration > Exim Configuration Manager.
For Boxtrapper:
WHM > Server Configuration > Tweak Settings and ensure "Enable BoxTrapper spam trap" is set
WHM > Packages > Feature Manager to ensure Boxtrapper is accessible from cPanel interface
You may then enable it within each desired cPanel account.
Thanks,