The Pending Inbox is located on the Inbox as a separate tab. It shows applicants have have started the application process but have not clicked "Submit".
If you don't have the "Pending" tab it means that it's switched off in Project Settings.
To switch the Pending Inbox on:
1. Click your avatar on the bottom-left to open the User menu.
2. Select "Project Settings".
3. Scroll down on the Project Settings page until you see "Casting".
Click the downward arrow to expand the Casting section. Toggle the "Pending Inbox" to blue (on).
For more information on the Pending Inbox see the Inbox Help Guide.