If by control character you mean characters with ASCII codes between 0 and 31 then the following query will find all records where col1 contains any of such characters:
SELECT * FROM my_tab
WHERE INSTR (TRANSLATE
CHR(0)) > 0);
This efectually translates all characters below ASCII code 32 to a character ASCII 0 by using TRANSLATE and then searches for any occurence of such character with ASCII code 0 by using INSTR.
ASCII a stupid question, get a stupid ANSI
24 hours in a day .... 24 beer in a case .... coincidence?