The EV databases have lot of information. You need to know how EV works internally to understand every single table and where EV stores the data. Obviously, this information is not public. However, you can install EV reporting or enable EV auditing as EV-Counselor suggested. In addition, there are several technotes with SQL queries to pull data from the EV DBs. If you need a specific set of data for your customers, we can try to assist you. I will try to answer your questions:
- How many database & mailboxes are enabling in EV for journaling?
Use SQL management studio to see the EV DBs: EnterpriseVaultDirectory, DBs starting with EVVS^ and Monitoring database.
- How many user’s mailbox enable and disable in last 3 months?
I am not sure if you can get this information, but you can look at the ExchangeMailboxEntry table.
- Which mail restore & deleted by user that kind of information I want?
There is a report in EV reporting that can provide you this information.
- How many time user mailbox quota hit for archiving in EV (as history)?
You need to review auditing options under EV server properties.
- How can i know the changes made by other person in enterprise vault server? For e.g. in policy and in setting
You need to review auditing options under EV server properties.
- Details about user PST migration report? For e.g. how many pst for each user mailbox has been migrated along with pst size and pst count, that kind of information I want?
For PST migration, EV creates a report under the Enterprise Vault installation directory > Reports.
If you need a specific SQL query, I suggest you to explore reporting and auditing first. If not, you can post the question here or just open a ticket with support.
I hope this helps.