The responsibility for data protection at CERN is decentralised and organised in a particular way: Controlling Services are accountable for their processing activities. Consequently, data subject rights are to be exercised with regard to the personal data held by a specific Controlling Service.
It is not possible to satisfy a general request covering "all the information CERN helds about me". Bearing in mind that CERN's service catalogue contains currently over 600 active services, granting such a request would involve a disproportionate effort.
Therefore you should identify the Controlling Services concerned, in order to formulate the desired request to access personal data.
CERN's Layered Privacy Notice contains the list of Controlling Services that have published their privacy notice, allowing you to understand which personal data they process.
In case you are not sure which Controlling Service is responsible for the processing activity you are interested in, the Office of Data Privacy is available to provide you advice.