sys.dm_tran_locks contains the locking information of the sessions
If you want to know a specific table is locked or not, you can use the following query
SELECT
*
from
sys.dm_tran_locks
where
resource_associated_entity_id = object_id('schemaname.tablename')
if you are interested in finding both login name of the user and the query being run
SELECT
DB_NAME(resource_database_id)
, s.original_login_name
, s.status
, s.program_name
, s.host_name
, (select text from sys.dm_exec_sql_text(exrequests.sql_handle))
,*
from
sys.dm_tran_locks dbl
JOIN sys.dm_exec_sessions s ON dbl.request_session_id = s.session_id
INNER JOIN sys.dm_exec_requests exrequests on dbl.request_session_id = exrequests.session_id
where
DB_NAME(dbl.resource_database_id) = 'dbname'
For more infomraton locking query
More infor about sys.dm_tran_locks