Well, that will also depend on your ability. By inference, I mean sometimes, we wish to learn certain skills we think are in demand but our capacity to cope may lag. By capacity I mean ability to grasp and also of the financial requirements and implications to cope with that which we desire to learn.

However, if you can, learn:
1. Blockchain tech
2. Certification in SQL
3. Trading

* The last option will always be in vogue. It has been in vogue even before the other two and many more that have phased out now.