Ask him to have :
1. Good communication skills
2. Good
test automation skills(any tool)
3. Atleast 1 programming language knowledge like C/Java
4. Atleast 1 database knowledge like Oracle DB.
5. Good overall testing concepts
6. Good problem/puzzles solving logic.
Needless to say these skills cannot be developed overnight,either he has them or he doesn'nt.....Of course, I will never tell you the exact questions I was asked,since I wouldnt want someone less deserving to have an undue advantage.