Question: Could you please tell me if I can call a C# event or method from javascript code in an ASP.NET web application?

Answer: 
You cannot directly execute a C# Event or Method. You can hit an endpoint via AJAX. This could be an ASP.NET MVC Controller or an .ashx handler.

Alternatively you can look at implementing something like SignalR, which via its Hubs, allows you to do magical things from javascript (and from the server, push notifications and things of that sort.)
You can't. C# is executed in the server side while javascript is execute in client side (browser).