There are two ways to gather this information.
OPTION 1). Query Users table in Spotfire Database
SELECT [USER_NAME] ,[LAST_LOGIN]
FROM [Spotfire_server_DB].[dbo].[USERS] (Query for MSSQL Database)
OPTION 2). From Action log database
Prerequisite : Need to install Action logging.
Use the following query to get the last login of users ( Query for MSSQL Database).
select t.user_name, t.LOGGED_TIME
from [sf_actionlog].[dbo].[ACTIONLOG] t
inner join (
select user_name, max(LOGGED_TIME) as MaxDate
from [sf_actionlog].[dbo].[ACTIONLOG]
WHERE (LOG_CATEGORY = 'auth') AND (LOG_ACTION = 'login')
group by user_name
) tm on t.user_name = tm.user_name and t.LOGGED_TIME = tm.MaxDate