How can I see all the purchase orders for a specific Part ID ?

There are actually two ways you can do this; the first is by going to the part history, the second is by searching directly for purchase orders associated with the part.

To view a part's history (which includes purchase requests, orders, and more):

1. Click Inventory | Parts 

2. Click on the part you want to view

3. Click History on the left, which will give you more information such as work orders, and scroll down to view all purchase orders / requests related to the part. 

To search directly for purchase orders:

1. Click Procurement | Orders 

2. Click Search and type in the Part ID