Wireshark is a useful tool for capturing and analysing network traffic. Out of the box it supports numerous protocols including AX.25, and can be extended to decipher many more,

In order to handle encapsulated AX.25 it's necessary to use a small script to tell Wireshark which ports it should expect to find traffic on, and to decipher it.

(source https://osqa-ask.wireshark.org/questions/41221/dissecting-ax25-included-in-udp-ip-payload-applying-existing-dissector/ )