The Data Explorer query in this post would be a good starting point for that: Data Explorer query to show progress towards trust level 3 requirements. To share that query with users, the query’s existing parameters could be hardcoded into the SQL. They should be set to match the parameters that you see on your site settings page when you search for TL3. A username parameter could then be added to the query so that users could enter their username.
The biggest problem that I see with this is that it would allow users to query the status of other users on the site. For that reason, I would be reluctant to give a group like the TL2 group access to the query unless some way could be found to set the query’s username parameter in the background based on the current user’s username. That would require a change to the Discourse code.