My sim registered as a professional but I don't know what he can do besides cyberwoohoo. I've looked for options to engage in professional activities, but that's the only one I've found.

Actually, any sim with access to a computer can cyberwoohoo.

A registered professional gets paid every time they woohoo, whether it be in person or cyber, with someone who is outside of their household provided the customer has enough cash (otherwise it's free for them). How much they collect from their customer each time is displayed under your professional's KamaSimtra skill tab and is a function of the professional's Renown score. The ingredients in that score, and therefore their rates, are KS skill and the completion of the major and minor special KS challenges, also listed under that tab.

It isn't much in the beginning. I think starting out with skill level 1, a Renown score of 2, and no challenges, the rate is §60 or something like that. It goes up quite a bit at the higher levels and can be very lucrative. If two professionals from two different households woohoo, the money flows in both directions and the one with a higher rate nets a gain.

Some customers also get strong moodlets, can be positive or negative, from woohooing with a professional.

Oh, I knew cyberwoohoo is available for non-pofssionals too.

So th professional's options are the same as other sims', but they get paid?

Oh dear-I'm imagining what happens when they also want to have a significant other as well as their career.

pofssionals=professionals+keyboard shenanigans.

Correct. If their significant other is part of the same household, no one gets charged. Jealousy and cheating issues...well, those are challenging if that's what you meant. Even more so if both partners are working professionals. There's even a Cheater challenge on the KS skill tab that give the same Renown points as the others but kicks up a hefty attraction penalty once completed (no one wants to be with a famous Cheater for the evening). This is above and beyond the game's scrapbook reputation system. There's also a Bike challenge that scores a point whenever a sim woohoos with someone else who has a partner of their own. I think those are the only two challenges on that list with both positive (Renown) and negative (lowers attractiveness) effects.

The balancing act is all part of the fun.