Track how many attempts were made to escalate to table locks (index_lock_promotion_attempt_count), as well as how many times escalations actually succeeded (index_lock_promotion_count).

Lock_escalations.sql

-- get from https://blogs.msdn.microsoft.com/sql_pfe_blog/2009/06/11/three-usage-scenarios-for-sys-dm_db_index_operational_stats
SELECT      TOP 3
            OBJECT_NAME(object_id, database_id) object_nm,
            index_id,
            partition_number,
            index_lock_promotion_attempt_count,
            index_lock_promotion_count
FROM sys.dm_db_index_operational_stats (db_id(), NULL, NULL, NULL)
ORDER BY index_lock_promotion_count DESC