I'm using Redactor v2.8.5. it doesn't render an unordered list in HTML? How do I fix it?
Redactor is perfectly capable of rendering an unordered list, so perhaps your question is a little unclear.
If you mean that there's no formatting button to format an unordered list, check that you're using an appropriate redactor config which allows the use of 'unorderedlist' in your field definition:
More instructions about how to configure Redactor in Craft can be found at https://github.com/craftcms/redactor