This is not possible: unlike for GPRS 3G/4G, the module is not listening to the network, it is only broadcasting messages, so you cannot get a Sigfox RF signal quality.
You can get back the received singal quality in a downlink message, as a answer to an uplink message, but if you cannot receive, it will be useless.
You can also monitor the received signal quality on the Sigfox backend.