Everyone has already mentioned the basics. What I would suggest that check whether he or she can read some existing code and understand it and how quickly then

Everyone has already mentioned the basics. What I would suggest that check whether he or she can read some existing code and understand it and how quickly then can do it. I just hate it when someone asks me give KT (knowledge transfer) of some project to another team and ask me to take them through code rather than high level design. I mean if you can't read someone else code and get the intent/design out of it how you are supposed to write good code yourself.