From the event dashboard, click on "Content" from the sidebar.

Now click on the “Agenda” page, which lists all the sessions added to the event.

Click on the 'Edit' section in the desired session on the session card.

You will now see all the details about the session. Click on the “Questions” tab on the left-hand side under session details. 

Click on the checkbox “approve new question manually” to enable the moderation feature for the session questions.

How to enable moderation so that only the questions you approve are visible to all attendees?