In order to check the blocked queries in SQL server, we can make use of DBCC OpenTran command which will result in details of the transaction which has blocked the queries.

So we have a below scenario where we are updating the records into the table using transaction as shown below:

Now we open a new instance of SQL server and try running SQL queries on the same table as shown below:

We can see that all the queries are blocked to table. So in order to check the blocking queries, we need to execute command DBCC OpenTran

script to check open transaction in SQL server:

	
SELECT
    [s_tst].[session_id],
    [s_es].[login_name] AS [Login Name],
    DB_NAME (s_tdt.database_id) AS [Database],
    [s_tdt].[database_transaction_begin_time] AS [Begin Time],
    [s_tdt].[database_transaction_log_bytes_used] AS [Log Bytes],
    [s_tdt].[database_transaction_log_bytes_reserved] AS [Log Rsvd],
    [s_est].text AS [Last T-SQL Text],
    [s_eqp].[query_plan] AS [Last Plan]
FROM
    sys.dm_tran_database_transactions [s_tdt]
JOIN
    sys.dm_tran_session_transactions [s_tst]
ON
    [s_tst].[transaction_id] = [s_tdt].[transaction_id]
JOIN
    sys.[dm_exec_sessions] [s_es]
ON
    [s_es].[session_id] = [s_tst].[session_id]
JOIN
    sys.dm_exec_connections [s_ec]
ON
    [s_ec].[session_id] = [s_tst].[session_id]
LEFT OUTER JOIN
    sys.dm_exec_requests [s_er]
ON
    [s_er].[session_id] = [s_tst].[session_id]
CROSS APPLY
    sys.dm_exec_sql_text ([s_ec].[most_recent_sql_handle]) AS [s_est]
OUTER APPLY
    sys.dm_exec_query_plan ([s_er].[plan_handle]) AS [s_eqp]
ORDER BY
    [Begin Time] ASC;
GO

Killing open transaction using Activity monitor

Using Kill statement to kill the running process.