Well, that really depends on what your interests are. You don't want to be stuck for multiple hours a day in front of a computer doing something you hate.
As of November of 2019, the top 100 fastest-growing skills on UpWork were:
- NET Core
- TypeScript
- Landing pages
- eBooks
- Android
- Electronic design
- Presentation
- Sketch
- Research
- Technical recruiter
- Bank reconciliation
- Slack
- Google Tag Manager
- Sourcing
- Amazon Web Services (AWS)
- Video post-editing
- LinkedIn recruiting
- Data visualization
- Interviewing
- Interior design
- System administration
- Kubernetes
- Data scraping
- Technical documentation
- Project scheduling
- Adobe Premiere Pro
- 2D animation
- Firebase
- Customer retention marketing
- Salesforce Lightning
- DevOps
- Selenium
- Accounts receivable management
- Microsoft Windows Azure
- Database design
- AutoCAD
- Usability testing
- C development
- Accounts payable management
- Lead generation
- Product descriptions
- Certified Public Accountant (CPA)
- Circuit design
- eLearning
- Google Docs
- Docker
- GitHub
- Redux for JavaScript
- Business planning
- Data entry
- Motion graphics
- Infographics
- Architecture
- ASP.NET
- Asana
- Instagram marketing
- Shopify development
- Search Engine Optimization (SEO)
- Architectural rendering
- PostgreSQL administration
- Salesforce app development
- Python
- Magento 2
- Link building
- MongoDB
- Bootstrap
- SEO writing
- Web scraping
- Animation
- Network security
- 3D rendering
- Agile project management
- Administrative support
- Data mining
- Internet research
- English grammar
- Squarespace
- Elasticsearch
- Startup consulting
- AWS Lambda
- Branding
- Media relations
- Appointment setting
- 3D design
- Bookkeeping
- Romance writing
- Budgeting and forecasting
- Product design
- Financial accounting
- Adobe After Effects
- Zendesk
- Accounting
- Virtual assistant
- Google Cloud Platform
- Postgre SQL programming
- Tax preparation
- Embedded systems
- Audio editing
- Google Analytics
- Amazon S3
As for the learning, you can't go wrong with youtube. You can literally find anything on there.
There are other resources like Udemy which will cost you a few dollars per course but its a good place to start if you have not idea whatsoever where to begin.