If some of us got in contact with a saliva of an infected cjd person, how would you test if you caught it?

You can't... but. Transmission of cjd through saliva is very unlikely & has not been reported. Furthermore spouse or family members of patient with cjd appear to be at no greater risk of the disease than the general population. There is no way to tell if cjd has been transmitted prior to disease onset. Once symptoms occur then can do tests such as mri, lymph node biopsy for vcjd, spinal fluid tests & brain biopsy.
You can not.. Currently there is no test for cjd. There is only the ability to confirm the disease after ruling out other diseases and with an autopsy of the affected person's brain tissue after death. The incubation period of cjd is extremely long. If you were infected, it could take 10-50 years before you experienced symptoms associated with the disease.