How do I display the Contact ID on User Dashboard?
There are a couple ways you could do this:

Create a report that shows the contact ID and name, make that report available on a user dashboard, then you can use the dashlet extension to place the dashlet on the end-user dashboard.

Take the Contact IDs and reimport them as the External ID, then display that in the Contact Dashboard as part of the member profile.

Write some code to pull the ID out of the database and display it graphically as part of a Membership Card. I do this on one of my Joomla sites but there's no reason why it can't work in Wordpress.

Example: