Which courses a professional network engineer should know? I want to know exactly. Including which programming languages a network engineer should know?

For network engineer, you need scripting language . Perl , python and tcl/tk are some scripting languages which are necessary for doing the automation. Currently the whole world is moving toward automation , whether is automation of configuration scripts or some scripts which will monitor the systems & alarm the network administration in case of urgency or automation of other work flow. Now one expects network engineer to sit in front of the monitor and keep watching it for any errors. So for all these purposes , it would be better if you focus on scripting language.