I am currently evaluating NodeJS and Microsoft ASP.NET Web Api for a REST Api implementation which will handle heavy traffic and although I can see how NodeJS can be scaled out with various additional modules and technologies I cannot find an example of how you can do the same with ASP.NET Web Api.
What is the best way or technology to scale out and load balance the ASP.NET Web Api to multiple servers?
You can scale out any Web Api applications, like you do with other ASP.Net application. You basically have two or more web servers and have a load balancer or traffic manager to handle request between them.
What is the best technology? Well, that is a matter of option.
My opinion is that the performance bottleneck is at the data layer. You should look at implementing some sort of in memory caching facility such as Redis to help with scalability there.