It is kept confidential. Well, if you are in good relations with boss (and your CEP is high) he or she might share it with you, but making U swear to confidentiality. Coz which boss wants to tell her/his staff about his/her low cep and subject herself/himself to staff not giving her/his best?
Sometimes through bosses nuances about colleagues/staff in work appraisals, and if you are discerning you can tell. Other times study your own or colleagues' performance and promotions (relative to age) you'll be able to tell. I find it rather apparent. Say, a relatively young one being promoted early whilst another more senior one later (in terms of two of their age) the first one obviously would have higher cep coz need more levels/times of promotion.