AxonServer doesn’t have an internal database. You can use the UI (running on port 8024 by default) to query for events. There is also a http api, and obviously you can use the AxonServerConnector to access AxonServer.
If you need to integrate with other languages, the first thing to ensure is that you use a serializer that serializes to a compatible format. Jackson creates prettty clean Json, making it highly interoperable.
At this point, we don’t have AxonServer connector implementations for other languages yet. The proto files for the connector are publicly available though, so you can generate stubs in any language supported by gRPC (which definitely includes .NET).
Hope this helps.