How to prepare for the job market during a (pure math) PhD
Here are a few things that might benefit both your PhD and your preparation for the job search:


Communicate with your advisor. Setting goals and making plans with your advisor will help align how you measure the success of your graduate experience. You can also report to your advisor about your progress towards these goals; accountability goes a long way. Finally, your advisor can help you prepare for and find a job in industry, but only if they know that's what you want to do!
Code and compute. If you don't know how to code, take some courses and learn how. If you do know how to code, keep improving your abilities. Computing is a valuable skill for research, since examples will help you make sense of new ideas and constructions. In industry, computing will be invaluable. As a mathematician, employers will want to hire you for your analytical skills. These skills will be much more useful to them if you are comfortable gathering, producing, analyzing, and communicating data that they care about.
Connect. If you have the opportunity, do an internship in industry. You may find things that you like or dislike about working outside academia, and you may gain new insights into your academic work. You should also try networking. For better or worse, who you know makes a big difference in finding jobs. Your advisor might have some contacts in industry, or your university might have an employment center that can help you with this.


As an aside, even low-dimensional topology might not be as far removed from applications as you might think. Differential geometry and algebraic topology both have applications to data analytics and machine learning. Depending on your exact specialty, topological data analysis could be an opportunity for you to apply ideas from your PhD to finance or whatever industry you decide to join.