None, this behavior is intentional.
Why does the Knox Workspace container hide my email content on the lock screen?
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Any device using a Knox Workspace.
[Issue]
Knox email notifications do not show any content, even if device notifications are enabled to show content on the lock screen.
[Cause]
For security reasons, content is hidden for Knox Workspace notifications. This is to make sure no one can read, record, or otherwise access the content of email notifications coming from your secure Workspace.
[Resolution]