[sql] Oracle query to identify columns having special characters

They key is the backslash escape character will not work with the right square bracket inside of the character class square brackets (it is interpreted as a literal backslash inside the character class square brackets). Add the right square bracket with an OR at the end like this:

select EmpNo, SampleText
from test 
where NOT regexp_like(SampleText, '[ A-Za-z0-9.{}[]|]');