Listing the Microsoft SQL Server configuration with the values set by mssql-conf?
There is no command line option to view what the values are actually set too, for now you'll have to check the file yourself

cat /var/opt/mssql/mssql.conf


However, it does not show the defaults. Stock, it has two options. One for sqlagent.enabled and one for EULA.accepteula. If you change one of those values as in the case of disabling CEIP,

$ sudo /opt/mssql/bin/mssql-conf set telemetry.customerfeedback false


Your conf file will look like this,

$ cat /var/opt/mssql/mssql.conf
[EULA]
accepteula = Y

[sqlagent]
enabled = false

[telemetry]
customerfeedback = false