The closest equivalent we have in the .NET API now is MapView.SpatialReferenceChanged, which tells you when the MapView is essentially initialized. API feedback on rendering progress is on the roadmap for the next major release.
Is it going to execute every time the map renders when i pan or zoom for example? Or one time only?
That occurs only when the spatial reference is set so in most of the applications that is only one time (in the beginning).
If you want to show indicator on every move/pan, currently there isn't easy way to do it if you have large variety of layer types in the map. If you are using service based FeatureLayers, you can use UpdateCompleted event on ServiceFeatureTable. If you are using local features, there shouldn't not be need for one.
How about Manipulation Started and Completed?
That event just tells you when the user starts/stops touch interaction with the mapview.
Retrieving data ...