How to get all fields from featurelayer or featureTable in ArcGIS Runtime SDK for .NET 10.2.4?
You can set to "*" the OutFields property of your underlying ServiceFeatureTable
Example:
<esri:FeatureLayer ID="MyFeatureLayer">
<esri:FeatureLayer.FeatureTable>
<esri:ServiceFeatureTable ServiceUri="http://sampleserver6.arcgisonline.com/arcgis/rest/services/Wildfire/FeatureServer/2"
OutFields="*" />
</esri:FeatureLayer.FeatureTable>
</esri:FeatureLayer>