Data quality metrics are all contained within result files. Depending on the job that produced the result, the result may contain different metrics. For instance, if you have a Value distribution analyzer in the job, your result will expose a "Value count" metric (and many more).
To further complicate things, some metrics are parameterized. A metric can be parameterized by either a column name or a query string . For instance, some analyzers (like the String analyzer or Number analyzer) record metrics for multiple columns at the same time. To retrieve metrics from these analyzers you need to provide a column name as a parameter. Other metrics like the "Value count" metric of a Value distribution require a string parameter, specifying which value to get the count of.