Which of the three professions is more promising: intellectual property lawyer, patent agent and intellectual property system auditor?

You have to understand the differences and main directions of the three occupations. There is nothing more promising than this. It depends on which one suits you better. Lawyers mainly focus on intellectual property cases, and more on legal work. Patent agents are mainly responsible for writing patent cases, and more on technical work. The auditor of the intellectual property system you mentioned is in charge of the macro layout and strategic policy of the entire intellectual property system, so you can choose which one you want.