I do a LOT of interviewing here, and for a while we were hiring ASP.NET people. Here's some of the questions that I asked them. I came up with these questions because you'd "just know" this stuff if you spent time working on a REAL WORLD ASP.NET site - through design, development, debugging, production debugging, and deployment.
Do they suck? Did I miss any? How do you think people did?
* From constructor to destructor (taking into consideration Dispose() and the concept of non-deterministic finalization), what the are events fired as part of the ASP.NET System.Web.UI.Page lifecycle. Why are they important? What interesting things can you do at each?
* What are ASHX files? What are HttpHandlers? Where can they be configured?
* What is needed to configure a new extension for use in ASP.NET? For example, what if I wanted my system to serve ASPX files with a *.jsp extension?
* What events fire when binding data to a data grid? What are they good for?
* How does ViewState work and why is it either useful or evil?
* What is the OO relationship between an ASPX page and its CS/VB code behind file in ASP.NET 1.1? in 2.0?
* What happens from the point an HTTP request is received on a TCP/IP port up until the Page fires the On_Load event?
* How does IIS communicate at runtime with ASP.NET? Where is ASP.NET at runtime in IIS5? IIS6?
* What is an assembly binding redirect? Where are the places an administrator or developer can affect how assembly binding policy is applied?
* Compare and contrast LoadLibrary(), CoCreateInstance(), CreateObject() and Assembly.Load().