Unfortunately, there is no way to add a second email address to an agent in Lansweeper.
As for workarounds, there are some, however they are not ideal.
If the boss is not an agent then the best option is to create a scheduled report alert. Using a report which shows all ticket assigned to the tech in the last X amount of hours with state Y. This report will be emailed to the boss on a set interval. It will only be sent when the report has a value.
If the boss is an agent, the easiest way is just for him to log into the web console and create a ticket filter for the tickets assigned to the tech.
As an alternative, you can use outgoing email templates for agents and subscribe the boss to all the tickets. The drawbacks of this is that the boss won't be automatically subscribed to new tickets, and, when outgoing email templates are enabled, they are enabled for everyone, unless all the other agents set their notification options differently (blue cogwheel in the top right corner).