How to find out the source which populates the table in SQL ?

Here are a few queries to see where/what is connecting to your box and then you should begin to narrow down where the table is being populated from.

Listing of connections

SELECT * FROM     sys.dm_exec_connections

Query that lists detailed info among that being the last executed sql query - from sql server - how to get History of queries executed with username in SQL - Database Administrators Stack Exchange[^]

Lists IP address and last ran queries.

SELECT sdest.DatabaseName 
    ,sdes.session_id
    ,sdes.[host_name]
    ,sdes.[program_name]
    ,sdes.client_interface_name
    ,sdes.login_name
    ,sdes.login_time
    ,sdes.nt_domain
    ,sdes.nt_user_name
    ,sdec.client_net_address
    ,sdec.local_net_address
    ,sdest.ObjName
    ,sdest.Query
FROM sys.dm_exec_sessions AS sdes
INNER JOIN sys.dm_exec_connections AS sdec ON sdec.session_id = sdes.session_id
CROSS APPLY (
    SELECT db_name(dbid) AS DatabaseName
        ,object_id(objectid) AS ObjName
        ,ISNULL((
                SELECT TEXT AS [processing-instruction(definition)]
                FROM sys.dm_exec_sql_text(sdec.most_recent_sql_handle)
                FOR XML PATH('')
                    ,TYPE
                ), '') AS Query

    FROM sys.dm_exec_sql_text(sdec.most_recent_sql_handle)
    ) sdest
ORDER BY sdec.session_id