How would trace-route help you find out where a breakdown in communication is?

A tracert or traceroute can help in that regard as you can tell exactly where the chain of connections stop. With this information, you can contact the correct people – whether it be your own firewall, your ISP, your destination’s ISP or somewhere in the middle. 

when we trace-route in communication, we can find where there is a brakdown from the last Ip adress receiving in the network. 

Traceroute will shows every router (hop) that the packet  reach  while traveling from source to destination, it can show:

1- the hop causing the delay.

2- if there is a routing loop.

3- if the packet is taking unexpected/ unintended route 

Well, frankly speaking, trace-route shows every hop the packet is traveling through to reach a destination, when I have a communication breakdown I can trace-route and check where is the packet dropping or even taking an unusual amount of time.