Or a fit fella to please the ladies!
It may be as loosehead suggested that this person is being a little lazy. He may perhaps know the answers but it is easier to get others to tell him than bothering to look in his notes. My suggestion if you have not already done so is to get him to come to you with an answer not a problem. It is a cliche but it works, as basically you get him to start to think about what he is asking and he should realise hopefully that he knows more than he thinks.
If you have tried this or it does not work, then my suggested next step is a serious word with the boss, telling him all the steps you have taken to try to help him and see if the boss will put him on a work improvement programme to see if he will start to improve.
Cheers Sue