It should not be too hard. Just check the luggage at MSY, and it should somehow make its way to HKT. Assuming that SQ operates similar in SFO as it does at LAX, you will need to get an SQ boarding pass at the SQ check-in counter at SFO. When you are there you have to show them your stub with your checked luggage, and they will located and retag it for the SQ flight. I had a problem with this once, but it turned out fine in the end. Not exactly sure how it will work with your TG connection, sorry.