Don't chase "profitable" right off the bat. Teach what you know best. If you're from a developed nation, "profit" can be a hard target.
You'll discover more as you go. Don't invest too much time and money at the beginning as well. Start with simple gear and straight forward techniques.
Online courses are created with the mindset that students learn something useful after watching every video, every section, and every course. Niche courses do better on Udemy I believe, "focus strategies for students" would sell well as compared to 'learning strategies" since the later is vague and doesn't attract a specific audience.