All tickets in your queue would be addressed in the criteria by selecting "Current Assignment is Current group" and if you wanted to see all unassigned tickets then you could add on "Current Assigned Analyst IS NULL."
You can create 2 queries using Query Designer.
1. counts of all tickets -> criteria is current group
2. Unassigned Tickets -> Criteria is current group and current assigned analyst is Null.
On WebDesk add a new gadget on the dashboard of type "Count Queries" and add the above created two queries to your list.
Something like below as an Example -