The 'questionnaire_attempts' table and all code that uses it was removed in release 3.5.1, database version 2018050102. If you upgraded to questionnaire release 3.6.1, you would have executed the step that removed the attempts table. If your code is trying to access that table, you have somehow replaced your questionnaire codebase with code older than release 3.6.1. You may want to ensure that your questionnaire code is reset to the 3.6.1 code.
Check to see what version is being reported on your site plugin page.
Check to see what version is being reported on your site plugin page.