Where do you connect the two leads of a shunt trip breaker?

Usually the breaker's shunt trip coil is tied to a corresponding current transformer that is sized to the amperage that is allowed to be passed through the breaker. These types of breakers can also be connected into a distribution monitoring device. If the monitor detects a phase reversal or phase loss or voltage rise or drop the breakers shunt trip coil is remotely energized and isolates equipment down stream from the fault.

Shunt trip coil circuits are also used as safety circuits where the situation calls for only one breaker to be energized at a time. If the second breaker is inadvertently closed, this would allow both breakers to be on, the second breaker's auxiliary contacts that are an internally part of that breaker will close the safety circuit and energize the shunt trip in the first breaker to causing it to open. So as you can see the two wires could be part of many wiring configurations depending on what situation calls for.