Already a doctor but not satisfied!

I know someone who has already finished his PhD but he is not really satisfied, and he wants to apply for another PhD program abroad his home country in Africa; do you think he may have chances to be accepted in a doctoral program? His big challenge also is to know if he should mention in the CV that he has already get a PhD diploma otherwise; it will be a problem because the professor may ask him what did he do in the four passed years? Do you think it will be a good idea if he applies again for another PhD program in order to learn more ? according to him; he has no chances to apply for a post doc comparing his CV to others ( in term of publications, communication …) Thank you.