I am circumcised and my penis has gone sort of numb. How can make it sensitive again?

Your penis shouldn't be going numb unless there's a problem with blood circulation, the nerves, or if you are masturbating too frequently.

You might want to start by greatly reducing your frequency of masturbating and lotion your penis daily with a good skin moisturizer. When you do masturbate or have sex, avoid dry and abrasive techniques and stick to using lubrication.

If that doesn't help after a few weeks, see a doctor. Just because you are circumcised is no reason why your penis should be numb. If that were true, the population growth rate among most Americans, Jews and Muslims should be zero, which simply isn't so.