Missing panic logs in /var/log/kern.log

I just triggered a panic, expecting that the logs will be visible in
`/var/log/kern.log` after reboot, but there are no logs present there.

Considering I have no access to the serial port, how do I know what went
wrong?

Is there anything we can do to make sure that the kernel log contains all
the messages until before reboot?

# sysctl kernel.panic
kernel.panic = 30

If more information is needed, please let me know.

Best Regards,
Manty