1. His new play has a certain je ne sais quoi.
2. He has that je ne sais quoi that distinguishes a professional from an amateur.
3. She has a certain je ne sais quoi that charms everybody.
4. Although he's not conventionally attractive, he has a certain je ne sais quoi which makes him popular with the ladies.
5. The place looks pretty old and crumbly, but it does have a certain je ne sais quoi.