Payment Reference

If I make a payment to the US will the recipient be able to see the extra reference?
If I make a SEPA payment to UK will the recipient be able to see my extra reference?

Should be safe for SEPA payments. For US SWIFT payments, it’s really hard to predict. Too many middle men, and standards that are stitched together, legacy banking networks … it depends on a specific combination of sender and receiver. I would say: most likely, the reference should appear at the receiver’s end.