Explanation
When managing SSH keys, the CPM stores the public key on the target server. The CPM generates a new random SSH key pair and updates the public SSH key on the target machine. The public SSH key is stored in the home directory of the privileged user on the target machine, usually in the file ~/.ssh/authorized_keys. The public SSH key is not stored in the Vault, as this would be redundant and unnecessary. The public SSH key cannot be generated from the private key, as this would defeat the purpose of asymmetric encryption.
References:
* Manage SSH Keys
* SSH Key Manager
* Use SSH Keys

Explanation
The purpose of the PrivateArk Database service is to maintain the Vault metadata, which includes the information about the Safes, accounts, policies, users, groups, and audit records that are stored in the Vault.
The PrivateArk Database service is a Windows service that manages the database files that contain the Vault data. The PrivateArk Database service is responsible for creating, updating, deleting, and backing up the database files, as well as performing encryption and compression operations on the data1. The PrivateArk Database service is installed automatically as part of the Vault server installation and can be configured using the DBParm.ini file2.
The other options are not the purpose of the PrivateArk Database service, although they may be related to other services or components of the Vault. The PrivateArk Server service is the service that communicates with the components, such as the PVWA, the CPM, the PSM, and the PTA, and handles the requests from the clients and components3. The Event Notification Engine service is the service that sends email alerts from the Vault, based on predefined events and recipients4. The Central Policy Manager component is the component that executes password changes, verifications, and reconciliations for the accounts that are managed by the Vault. References:
* Server Components - CyberArk, section "The PrivateArk Server process (Dbmain)"
* DBParm.ini - CyberArk, section "Main parameters"
* Server Components - CyberArk, section "The PrivateArk Server process (Dbmain)"
* Event Notification Engine - CyberArk, section "Event Notification Engine"
* [Change Passwords - CyberArk], section "Change Passwords"