Hi,
In your workflow BASIC DATA setting where you insert your business object and workflow start event, there is an option/button C for inserting the start condition for workflow. There you can create a condition based on your specific plant and sales org. attributes (values) from your business object BUS2009. I can see that business object BUS2009 has got an attribute SalesOrganization, this will give you sales org. number. similarly for plant there must be an attribute in your business object BUS2089. just drill down the Item attribute and Use Items.Material.PurchaseRequisition.Plant for plant value.
Regards,
Ibrahim Ansari