I guess with such questionnaires, the whole discussion is more relevant than the answers to the questions. Do you let them take the test in written or in an interview? If it's an interview, I find your questions quite nice (except #1).

Question 2 could lead to discussion about personal coding standards, question 4 could lead on to discussion about which modules you use, whether you've written any yourself etc. Likewise, an answer to question 6 that only explains the return values of <=> would be quite disappointing. A good answer would involve a few applications, like e.g. sort {$b <=> $a} and maybe even some personal experience where you got bitten by using it wrongly. A discussion like this can tell you a lot about a developer.