How to self educate yourself? How to know the right program for obtaining knowledge? When I begin reading a book, I easily switch to ?

Well, you say that you cannot focus and easily switch to another topic. This is fine, but what you end up as is someone who knows a little bit about a lot of things. This is great for trivia games, but you might want to decide to up your game and acquire some expertise in one of your interests. In 2020 it's not that difficult to find out what the tenets of any particular discipline are and begin by reading those. The other problem you face is the lack of discussion and challenge you would get through studying these things formally in university - tests, reports, class discussions, etc. While these are challenges, there's nothing to stop you. I suggest you go for it! You can find most everything you need at your public library. 

The best advice I know about this is from the philosopher Mortimer Adler, whose books include the classic How to Read a Book. It's not how many books you read. It's how many good books you read and become friends with. It's all a matter of finding the best books. 

Here's something that makes reading easier. Never read a non-fiction book from start to finish. It's easier to find out what you're going to read before you read it. Start by reading the table of contents. Start reading a chapter by look at things that tell you about what's in the chapter - headings, sub-headings, pictures and their captions. Always read with a pencil in your hand.One way to underline is to read quickly just underlining some interesting phrases and sentences. Then you go back and study the chapter carefully. Knowing how to underline is very useful. You don't want to underline too much or too little. You want to get the main facts. When you've done a good job of underlining a chapter, you'll be able to read the underlined parts and they will make sense like reading the book. When you write margin notes, they can tell you where things are in the chapter. It's very good to have your own ideas about what you're reading and write them in the margins.