Currently, it is possible to query related records on feature services in the ArcGIS Online Map Viewer ONLY- not in any web templates or App Builder. When consuming the same web map with a hosted application or Web AppBuilder, the option to Show Related Records is not available.
This functionality is available in Flex, and Esri is not supporting Flex actively anymore.....so what are we to do if we have a need to show related records?
Web apps are how agencies communicate data to the public, not through the map viwewer page. Not being able to see ALL of the data in a web map is a huge limitation.
Support for related records should be added so users do not have to lose functionality for being good little Geogeeks and moving toward AGOL web apps and Web App Builder.