Hi,

the file should be in the SSSD log directory, so typically
/var/log/sssd/p11_child.log.

Since it does not exists, p11_child was not called to validate the
certificates. In this case sssd_ssh.log is the only source of
information. Feel free to send the file or the part of the log file
which covers the time where sss_ssh_authorized_keys was called.

bye,
Sumit