Question:

Why an Approval Pending event does not appear in the Items to Approve List section of a delegated approver’s home page?

Answer:

Events Management workflows support delegate approvers, users authorized by the administrator to approve an event on behalf of another approver but Salesforce only allows users directly assigned as approvers seeing the approval pending records in the Items to approve list of the Home Page.

The following workaround provides similar functionality for the delegated approvers:

1. Create a checkbox field on the object for approval and make it read-only to users.
2. Create a Field Update on Initial Submission of the Approval Process to check the box (The box is checked whenever a record is in-process).
3. Be sure to create another Field Update upon Final Approval/Rejection/Recall so that once the record exits the process, the box is not checked.  
4. Create a list view on the object where the view criteria Checkbox is true.

As a result of these changes, the delegate approver can see a list of records to approve in the newly created List view.

Related Documentation:

CRM Help Documentation: Approval Flows Integration