Is there a way to await an event (commandCallBack)?

You can use AfterRender client-side handler (AfterRenderJavaScript property in MVC DayPilotSchedulerConfig).

This script will get called after every update (including the initial rendering). You can also pass custom data to it using Update(data) call.

Example:

<%= Html.DayPilotScheduler("dps", new DayPilotSchedulerConfig {
  BackendUrl = ResolveUrl("~/Scheduler/Backend"),
  AfterRenderJavaScript="afterRender(data, isCallBack);"
  ...
%>

<script type="text/javascript">
function afterRender(data, isCallBack) {
  if (isCallBack) {
    alert('Rendering finished (after callback)');
  }
  else {
    alert('Initialization finished');
  }
}
</script>