Okay, need to use DEPTID and LOCID fields and the Department and Location pk values in the DMax. Add those fields to the Requisition query and add textboxes bound to those fields.
=DMax("[OrderDate]","Orders","DeptID=" & [DeptID] & " AND LocID=" & [LocID])
Or use the Requisition query as is as the data source for the DMax.
DMax("OrderDate", "Requisition", "Department='" & [Department] & "' AND Location='" & [Location] & "'")
Another option is in Report header or footer a textbox with:
=Max(OrderDate)