See currently running queries in SQL Server 2012

SELECT r.start_time [Start Time],session_ID [SPID],
DB_NAME(database_id) [Database],
CASE WHEN statement_end_offset=-1 OR statement_end_offset=0
THEN (DATALENGTH(t.Text)-r.statement_start_offset/2)+1
ELSE (r.statement_end_offset-r.statement_start_offset)/2+1
END) [Executing SQL],
FROM sys.dm_exec_requests r
OUTER APPLY sys.dm_exec_sql_text(sql_handle) t
WHERE session_id != @@SPID — don’t show this query
AND session_id > 50 — don’t show system queries
ORDER BY r.start_time

This query is great at finding locking queries like the one below:

To fix this, either add “(NOLOCK)” table hint to allow the select to run while the update is happening or kill the offending process using “KILL” command followed by the SPID