people can write and create blockchains in many languages. however most are wrote in C++
so to get the most understanding and able to read/review existing blockchains where you can then use them for idea's for your own, learn C++

just be aware. there is not much talent/skill//jobs where a 'script kiddie' just reads and copies code. no one sees that as valuable. true skill is in learning the math and cryptography where you can truly get into the security details of blockchains and not just the easy database and message package and GUI stuff

so if seriously wanting to invest time and money into becoming a valued dev. learn about cryptography as part of your education

Start with the basics. The first place you would want to start is learning a programming language. I would recommend C, although its not really relevant to most Blockchain programming, its really helpful and makes learning other programming languages much easier. There are many free courses online as well. So thats something you could easily look up on your own.

Understanding Blockchain is something that you could also look up. But I also recommend going through the development sections of this forum to see what the other developers are doing. Maybe they will even let you participate in their projects.

i know it is very hard to be so without any basic knowledge , but i would like to start from the bottom.anyway thank you for idea

Yes, it would be very hard but when you study it several years from real experts, it could be a huge achievement.
I wish you very good luck and a good university for your study. 

Bitcoin is always in need for good ideas and Bitcoin core developers are happy to receive some ideas.

Since you wisely worded the topic as 'blockchain based developer' that implies that you already know that using a blockchain is NOT just limited to cryptocoins. Blockchains are being used to replace conventional databases that are used in a myriad of applications where goods and records need to be securely tracked and that information permanently stored. Examples are in shipping logistics, food production, state and municipal records, etc.

For those applications the current pool of programmers who know how to code for them is very small meaning salaries for talented programmers are huge. BTW: this is the same situation for AI programmers - huge demand but few people who know wtf they are doing.

That said, it means that:
a. you need to learn how to code c++/python/java/etc. If you can wrap your brain around that then you will have a very good start.
b. you need to learn databases - much of what goes into designing a database application applies to blockchain tech as well
c. you need to find universities that have blockchain (and or AI) programs.
d. somewhere in all that you also cover at least a working knowledge of cryptography, 'c' should have the needed courses for it.

It is NOT impossible but it does mean that you need to learn quite a bit. Of course that applies to ANY technical career you want to pursue...

Right approach! One can not start blockchain developer without having basic concepts cleared. Academic approach helps greatly in clearing the concepts.

If you want to be a blockchain based developer, the first and the most basic requirement is to have the knowledge of blockchain. As you said you have no prior knowledge of it, you should first take a professional online course and read books about blockchain developing. When you start learning, remember that computer, coding, and development, is not just theory but a grater practical application. Being a blockchain developer is not easy, the concept of blockchain in itself is very huge and complicated. It will test your dedication and understanding skills. But if you are really focused on achieving this goal, you can definitely develop your own coin one day.

You can become a great Blockchain developer if you are ready to give in all that is required.
First, you cannot become a blockchain developer without knowing how to code, and not just knowing how to code, but you must know how to write some programming languages and most importantly of them C++, solidity.

One place I know that have some zero to hero blockchain developer courses is Udemy, courses on Udemy are for sale, and I must let you know that some of the courses can be quite expensive, but I can assure you that if you get a good blockchain developer course and follow it diligently, you will actualize your dream of becoming a good blockchain developer.

Learn the basics first, the foundation. You can start to practice coding in any programming language at first just to familiarize some basics like some logics because later on you can use this knowledge on some programming language. After that, you select your programming language and stick to it until you master it just like others said, C++.
There are already a lot of self-taught programmers these days just because of the internet, you can learn on the internet.