Say that you have an IPSEC Between 2 Palo Alto devices (or at least 1) and you want to know what is inside those ESP Packets.
you could capture Protocol 50
To get the keys you will need to raise the dump level: debug ike global on dump
Send some traffic over the VPN Tunnel, and you will see in the IKEmgr the Encryption Key and the Authentication key used on that SPI
see in the image above the first packet (1) as ESP
make sure the SPI value set-in Wireshark is in LOWER case
After Wireshark decrypts it, we can see that ICMP traffic was sent out via the tunnel interface encapsulated on ESP, and that an ICMP message as the payload timing out