Get configuration of running sshd
It is not possible to dump the configuration from running sshd, but you can instruct the sshd to parse the configuration and dump the resulting applied configuration options including default values from the default configuration file. There is -T switch for that.
There are commandline options overriding sshd_config
You can use -f switch to read the configuration file from different file.
Everything is well documented in manual page for sshd.