I thought I could import a CSV file into ArcGIS online and then add XY coordinates to the attribute table- but, it seems like one needs to be using Desktop or online Pro in order to be able to do that. I don't see that ArcGIS Online allows the user to add the XY coordinates as one can do using Desktop. Is this correct?
I would recommend up voting this idea on Geonet! At the moment, you cannot add XY coordinates to a web layer or CSV in AGOL. You can however, pull in the web layer to Pro, and run the Add XY Coordinates tool on it there.
Hope this helps!