How high does a cooking temperature have to be to kill creutzfeldt-jakob disease?

No temp is ok: Creutzfeldt jacob disease is transmitted by a small agent called a prion which is an abnormal protein which can replicate by changing the structure of protein like it when ingested. It is not destroyed by the normal temperatures used in cooking or even sterilizing, and therefore the disease can not be prevented in this fashion.

No one knows: If someone is trying to frighten you about the safety of ordinary beef, they're playing with you. During the "mad cow disease" (not cjd which by definition isn't transmitted) epidemic in england, cooking did not seem protective. Thankfully, the epidemic seems to be over. Fears are understandable -- after "jaws", people stopped swimming in lake michigan. I believe that beef is safe today.