Yes, it’s possible to wire two shunts in series in one battery system.
Typically, a second shunt is needed to monitor a different circuit.
Suppose you need to use two shunts in a single battery system to measure the current associated with specific devices (both for charging and discharging). In that case, you can place each shunt in the specific path of the device you want to monitor.
You should note that both positive battery references come from the main battery. Otherwise, there will be a voltage drop, which is not desired.
If you have two shunts, one for monitoring the battery’s capacity and another for tracking an inverter, you must wire them in series. This is because a parallel setup will split the current flow in two.
If you have an older shunt but want to keep it, then you can wire your new shunt like the diagram above and have two battery monitors for two locations.