Query to Find Junk Characters in table

SELECT   okh.contract_number, okl.line_number, okl.attribute6, okl.sts_code

    FROM okc_k_headers_all_b okh, okc_k_lines_b okl

   WHERE okh.ID = okl.dnz_chr_id AND okl.attribute6 IS NOT NULL

  HAVING REGEXP_COUNT(okl.attribute6, '[''~!@#$%^&*(),+=}{;:><?]') >= 1

GROUP BY okh.contract_number, okl.line_number, okl.attribute6, okl.sts_code

once it is identified remove it by updating table using below query  

REGEXP_REPLACE(okl.attribute6,'[''~!@#$%^&*(),+=}{;:><?]',NULL)