The quiz can be found here: XHTML Quiz — ManuelBieh.de (beta). Some things to note:
eXtensible HyperText Markup Languageas the quiz suggests.
blockquote requires block level element content when following the strict version (and future) of HTML/XHTML.
p element for a line break is valid, but not correct. It was not clear to me what was meant. That may be due my lack of knowlegde of the German language.
DOCTYPE. Just like XHTML 1.1 Strict as DOCTYPE does not exist. I am therefore unable to answer that particular question as it uses radio controls where I need checkboxes.
DOCTYPE is not an element.
Still a great idea though.