By default, when you ask a question to a client, it is visible to all the client users. If you have certain questions that are not meant to be visible to all the users, then you can use this feature of Question privacy.

To enable the feature, see the steps below:

Go to the Settings (⚙ icon) ➝ go to the Question Settings ➝ Turn on the Question Privacy feature, and it's done.

To make the question private:

Click on the Lock icon available in the Ask question pop-up ➝ choose Private, and the assigned user will only see the question asked.