I'm the OP. Here is some more info:
Thanks for the suggestions. Trading directly on a brokerage account owned by the client sounds best so far.
I'm a non-US citizen, currently resident of Hong Kong.
I want to be able to charge performance/incentive fees, say 12% of the profits.
Do I need any special licenses to do this for non-US clients?
What about US clients?
If you're a non-US citizen residing in Hong Kong, and your clients are also non-US clients, then it's probably best to check with Hong Kong laws as the op suggested.
For US clients, you may want to ask the FINRA call center regarding licensing.
FINRA Call Center
Main FINRA Phone Number: (301) 590-6500