It's hard to tell what data you're even working with, but the standard object name is simply [`Pricebook2`](https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_objects_pricebook2.htm) (no underscores). If you are trying to insert a record looking up to this object (such as [`PricebookEntry`](https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_objects_pricebookentry.htm)), the name of the lookup field is `Pricebook2Id`.