I'll frame this question using the sample code.
When doing a QueryFeaturesAsync on the feature table, the resulting feature has only 3 attributes populated (NAME, OBJECTID, STATE_NAME).
There are quite a few more fields available as shown here. And, of course, this fails:
var abbrev = feature.Attributes["ST_ABBREV"];
How do you execute QueryFeaturesAsync and get all of the attributes returned?