1) If I had earned a broker fee for a transaction overseas and the fee was deposited in my overseas account, then do I have to pay taxes in US?
2) If one day I want to transfer the money to my US account, will I have any tax liability?

A U.S. citizen or resident must report worldwide income on his/her tax return. So the broker fee earned by you must be reported on your tax return.
Another filing requirement is Form TD F 90-22.1. Your U.S. Tax Return: U.S. Citizen or Resident with Foreign Income