See the examples page in the documentation. There is one example using the ThingSpeak communication library to read a thermistor and output the temperature. It also shows how to read data from a channel in the form of calibration parameters.
The moisture monitor example shows you how to write to a channel without using the library. You can modify the command to write into a read command using the API commands for getting field information from a channel. Or for getting all the channel feed info.