Comments let your respondents type in a custom reply without interrupting their workflow. Here's what will happen if you turn comments on - they work with Single & Multiple answer selection questions. We've known it working great with the "Other" answer option.
Go to the question you'd like to enable the comment, click the speech bubble 🗨 icon next to the answer:
How can I use comments with other types of questions?
If you are using other question types, such as NPS, rating, smiley scale, you can use survey logic to create an open-ended response effect.
(1) Add a text answer question to your survey
(2) Go to the Logic tab of the question you'd like to add a comment option
(3) Change the next step of the answers you want your respondent to comment on as the text answer question you've just added: