How can i hear do re mi fa sol la si?

Question

How can i hear do re mi fa sol la si?

Answer 1

just say it

Answer 2

Buy "The Sound of Music" soundtrack

Answer 3

You mean: do re mi fa so la ti do?

In order to "hear" it automatically in your head and sing it accurately, you need some musical training (lessons) and experience, preferably in your youth. Why? Because once when you get to adulthood and have no musical experience, you are unable to "hear" it.