It seems you are using the census income dataset. If you want to learn more about KNIME and especially machine learning I compiled a few links in this entry - the dataset is also used in one example.
Also in the next entry @ipazin mentions the free udemy course on KNIME which also has a machine learning part:
Then if you are free to use any method like R or Python you could still use KNIME as a wrapper and to evaluate the results in a standardized way.