SELECT
    w.query AS waiting_query,
    w.pid AS waiting_pid,
    w.usename AS waiting_user,
    l.query AS locking_query,
    l.pid AS locking_pid,
    l.usename AS locking_user,
    t.schemaname || '.' || t.relname AS tablename
 FROM pg_stat_activity w
       JOIN pg_locks l1 ON w.pid = l1.pid AND NOT l1.granted
       JOIN pg_locks l2 ON l1.relation = l2.relation AND l2.granted
       JOIN pg_stat_activity l ON l2.pid = l.pid
       JOIN pg_stat_user_tables t ON l1.relation = t.relid
 WHERE w.waiting;

SELECT
...