The simplest way is to use a « CC2531 USB sniffer » dongle as indicated on the zigbee2mqtt.io website
Some people apparently use CC2530 dongles as well.
Since the basic sniffer does not contain the zigbee2mqtt firmware, you have 2 options:
Buy a basic sniffer + CC debugger that will allow you to flash the firmware.
This second option has an equivalent price to the first but can quickly become very economical if you have several dongles to flash (to increase the range in a large house, for example) because you will reuse the CC debugger.