It's hard to find.
If anyone has such data, they would like to monetise on it. Or you can start a search for this data on country-wise which you think can represent the entire world.
You can also look for apple, Facebook, Microsoft, etc., and from there you ca guesstimate.
It depends on what kind of data you're looking for. Remember there's a huge difference between total market size and addressable market. I really hate when someone pitches me and talks about a $91B market. There's no way they're ever going to get a large piece of $91B, and it turns me off to have them try to impress me with a big, unreachable number, especially when speaking globally. Each country/region would need a completely different marketing strategy and most of the time they haven't validated the strategy for even one country.
If you're specifically talking about video conferencing software for elearning, there has been plenty of discussion both in the investment industry as well as in the education space about what the landscape looks like today. You can find it in everyday news if you make an effort.
Yep. Why do you need it? For a business plan or product development?