You can use the following SQL query to find workflows inside the Nintex Content database based on their state. Simply modify the "WHERE" argument to look for workflows in other states.
SELECT DISTINCT i.workflowname, i.webid, i.siteid, i.listid, p.CurrentActivityTitle, p.TimeStamp FROM dbo.workflowinstance i inner join WorkflowProgress P on I.InstanceID = P.InstanceID WHERE i.State = '2'
Here are the different states you can query:
when 2 then 'Running'
when 4 then 'Completed'
when 8 then 'Cancelled'
when 64 then 'Error'