To see how many and which panelists have answered to a single query, you can review it from QUERY ACTIVITIES.

Open the ADMINISTRATION -tab. Under the PROCESS header, there is a section QUERY ACTIVITIES. Click on it.

Now you can will the QUERY ACTIVITIES view in front of you. You will see the QUERIES on the left, and below it, all the queries of your panel.  Select the query whose usage information you want to view.

On the right side, you will now see the information of the  panelists who have answered to the query. The panelists are listed in alphabetical order.
Behind the name you see when the panelist was last logged in and when she/he responded to that query.

By clicking the LAST LOGIN, the panelists are organized by login, either from the latest to the earliest or from the earliest to the latest. By clicking ANSWERED, the panelists are organized by the responding date.