Below are 40 questions you can ask a person specifically from HTML 5 perspective.
http://www.codeproject.com/Articles/702051/important-HTML-Interview-questions-with-answe
What is the relationship between SGML,HTML , XML and HTML ?
In HTML 5 we do not need DTD why?
If I do not put will HTML 5 work?
Which browsers support HTML 5?
How is the page structure of HTML 5 different from HTML 4 or previous HTML?
What is datalist in HTML 5 ?
What are the different new form element types in HTML 5?
What is output element in HTML 5?
What is SVG?
Can we see a simple example of SVG using HTML 5?
What is canvas in HTML 5?
So how can we draw a simple line on Canvas?
What is the difference between Canvas and SVG graphics?
How to draw rectangle using Canvas and SVG using HTML 5 ?
What are selectors in CSS?
How can you apply CSS style using ID value?
What is the use of column layout in CSS?
Can you explain CSS box model?
Can you explain some text effects in CSS 3?
What are web workers and why do we need them ?
What are the restrictions of Web Worker thread ?
So how do we create a worker thread in JavaScript?
How to terminate a web worker
Why do we need HTML 5 server-sent events?
What is local storage concept in HTML 5?
How can we add and remove data from local storage?
What is the lifetime of local storage?
What is the difference between local storage and cookies?
What is session storage and how can you create one?
What is difference between session storage and local storage?
What is WebSQL?
Is WebSQL a part of HTML 5 specification?
So how can we use WebSQL ?
What is application cache in HTML5?
So how do we implement application cache in HTML 5 ?
So how do we refresh the application cache of the browser?
What is fallback in Application cache?
What is network in application cache ?