In Reply, you can quickly find people who are/are not on a specific list by creating a smart filter on the People page:
On the People page, click ADD FILTER.
In the Filter name field, enter the name for your filter (optional).
In the Property field, select List from the drop-down menu.
Select the Is/Is not value.
In the Select list field, select the desired list from the drop-down, or start typing the name of your list or a shared one (if you are using Team Edition in the Public mode).
Click Save to display the results.
Please note that if you select Is set/Is not set, the system will return all people who are/are not in any list.