On the Purchase Order there is a Native field called "Memo" is there a way to see all transaction types (po,invoice,bill,bill credit ,etc) that have this native field on them? in addition similar to where you can see a list of all custom fields created, can you see all the native fields in NS?

You could use the records browser, not strictly in NetSuite but it will tell you all native fields, if they are searchable and the columns for sublists / searches etc https://system.eu1.netsuite.com/help/helpcenter/en_US/srbrowser/Browser2019_1/script/record/transaction.html