Say, employees use the Company's Credit cards, and you have questions about the categorization of some of the transactions. You don't want to show those transactions to everyone but only to those to whom it pertains. So you can ask private questions.

To set the question private, first, please enable this feature from the setting.

Settings > Question Settings>Turn on the Question Privacy feature

Public questions will be seen by all the client users. To set it Private, Click the Lock Icon and set the question as Private. Only the assigned user will see the question asked.