1) In the blue ocean shift, it mentions the importance of being in the field to assess pain points.
If my field (personal development) people just access online courses from the click of a button, would being in the field involve me just watching people download a course?
I enjoyed the blue ocean strategy quite a lot.
It'd be more like talking to people in your market that have bought your product or a competitor's, or are interested in buying.
2) I'm brand new to business so I have no existing customers to interview, is this a problem?
Not necessarily, if you can find a way to talk to your market then you can work on finding a blue ocean to create.
3) What would be the best way to find non customers to interview? do I have to find strangers and ask to interview them? Or just post questions on forums for people to answer?
There isn't really a best. Go to where they are and engage with them how they like to be engaged. If they're on forums, then go to forums. If they're on social media, then go to that specific social media. If they're not online much then seek them out physically.
4) How many people approx would I have to interview/observe in the field
That's not a knowable question. It also doesn't matter.
Figuring out a blue ocean isn't direct. But the only way to find one is by getting to deeply know a market you wish to serve, as well as what is currently being offered to them.
If you're really serious, then get started! As you start to talk to people and get positive reinforcement, you'll find it getting easier and easier.