Several example clients are provided with the MDK. You can find these at
~/mdk/bin/shared. Generally, they will work with any of the development Profiles (though some features may be missing in some configurations).
This is by far the most comprehensive example, showing how to access all of the upstream signals and to command all of the downstream signals.
This client shows how to manage streaming of audio to the robot, keeping the buffer stuffed to ensure continuous playback.
Other clients illustrate how a user client might begin to be constructed, listening to and sending to various of the sensor and control topics.
If you want to develop a client in C or C++ rather than Python, you will find the headers you need at