Because it's under the approval checklist button on the top right hand side of your screen.
We've recently made changes to the approval checklist button to provide you with more room to fill in longer checklists when it's open. To do that, we've hidden all checklists under a modal. Click the Approval Checklists button in the top right hand corner of your screen to open the checklist.
Because you weren't added to the submission in a user group.
Approval checklists are a great way to ensure that users have checked each and every aspect of someone's work before officially approving it in the system.
If your organisation is using approval checklists, and if a blanket organisation-wide checklist is not configured for your company, you need to be added to an approval submission request in a checklist-configured User Group. If you usually see these checklists and aren't seeing them now, it's likely the submitter has added you to the approval trail as an individual (ie by typing in your name directly).