Do you think there be sex work in a sexually non-repressed society?

I absolutely agree that there would still be sex work. Like the saying goes, "You don't pay a prostitute for sex, you pay her to leave afterwards". While this is not necessarily the case for every man, they are paying for something they are not finding in other women. Sometimes that is actually the sex itself, other times it is anonymity, reliability, a boost to the ego, sex without emotional consequences etc. There will always be a place for those wants, no matter what kind of world we are living in.

Of course there would be. In societies where it is legal, and where it was, like many ancient societies like Rome, Greece and Egypt, certain types of prostitution were not only legal but encouraged. The Ancients had temples where "barren" women would go to work, and hopefully somehow finally get pregnant, and sometimes it worked! Whether to get pregnant or simply serve society, it was considered an honor to work in these temples and houses.

People will always pay for sex and always pay to see others have sex. Legalizing it will just help reduce underage workers, forced workers and corruption.

There absolutely would be.

But if it was a sex-positive world that also had no human trafficking, no poverty and no drug addiction, there would be fewer sex workers.

And those few sex workers would have great pay and a lot more control over how they wished to practice their profession.