This is a list of topics/questions you might want to think about from a web software engineering standpoint.
Can you describe a typical web application stack?
Do you write code following any sort of coding standard? What do you use?
How do you decide whether to 'build or buy' (or in the web world, to build or use open source)?
What sort of version control systems have you used? What do you like/not like?
Particularly for web applications, how do you handle data validation?
What sort of techniques do you use to validate data?
What should you validate?
At what level of the application stack should you validate data?
What else do you do in order to make sure that your application is secure?
Have you done any unit testing? What are some of the principles of writing a good unit test?