Please explain why you need a trigger.

If you are asking "How do I do EXECUTE IMMEDIATE in SQL Anywhere 10?" here is a demonstration using a stored procedure:

CREATE TABLE trans_comp (
   batch_no INTEGER NOT NULL PRIMARY KEY,
   day1     INTEGER NOT NULL DEFAULT 0,
   day2     INTEGER NOT NULL DEFAULT 0,
   day3     INTEGER NOT NULL DEFAULT 0,
   day4     INTEGER NOT NULL DEFAULT 0,
   day5     INTEGER NOT NULL DEFAULT 0,
   day6     INTEGER NOT NULL DEFAULT 0,
   day7     INTEGER NOT NULL DEFAULT 0 );

INSERT trans_comp ( batch_no ) VALUES ( 1 );
INSERT trans_comp ( batch_no ) VALUES ( 2 );
INSERT trans_comp ( batch_no ) VALUES ( 3 );
COMMIT;

CREATE PROCEDURE update_day ( 
   IN @batch_no  INTEGER,
   IN @colday    VARCHAR ( 2 ),
   IN @tothour   INTEGER )
BEGIN
   DECLARE @sql LONG VARCHAR;
   SET @sql = STRING (
      'UPDATE trans_comp SET day',
      @colday,
      ' = ',
      @tothour,
      ' WHERE batch_no = ',
      @batch_no );
   EXECUTE IMMEDIATE @sql;
   COMMIT;
END;

CALL update_day ( 2, '4', 10 );
SELECT * FROM trans_comp ORDER BY batch_no;

batch_no,day1,day2,day3,day4,day5,day6,day7
1,0,0,0,0,0,0,0
2,0,0,0,10,0,0,0
3,0,0,0,0,0,0,0