View - Audio Bus Tracks.
The shortcut key is b.

From the online help menu:
From the View menu, choose Audio Bus Tracks to toggle the display of audio bus tracks at the bottom of the timeline. An audio bus track exists for each bus or assignable effects chain in your project and serves as a timeline representation of each bus or assignable effects chain.
You can use bus tracks to automate volume, panning, and effect parameters using envelopes.
The controls in the bus track are duplicated on bus or assignable effects control in the Mixer window.


Mike