Assuming you are customizing the case portal to view certain fields and want to fetch it, the following fields are associated with your query :
This field is available on Case Object which is of type LookUP(Contact).
Using this id, you can retrieve contact record and look for the field name
on the contact object.
Also, available system and custom fields on any object, one can check it in salesforce. go to setup > object manager > search for the object you want > fields and relationships.
Let us know if you have further questions. @RaunakB @AshishKe
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