I think certain jobs like copywriter are at extreme risk to AI. Fitness trainer seems highly unlikely to be a remote job. I think the best skills would be related to coding and programming. They pay the best and seem to be in high demand. In regards to teaching English, beyond just the certifications, there are many people doing this so I imagine it isn’t going to be the best paying. In my research, seems like teaching English can get you $10-$15 dollars/hour. This could work in maybe a lower cost of living country. So be realistic. I also imagine it would be exhausting if you had like 5 or 6 customers a day. 

Remember, this is list of links just to get you to think about learning a skill. Only you know if this is something you want to do. But unless you have a lot of financial resources or a passive income source, you will need some solution if you want to live abroad.

In a perfect world, you would would like these skills or acquire your clients before you decided to move abroad.