获取未编组的json struct中的键的值

First of all, I have read a lot of questions, I only find two similar questions but I can't add a comment (reputation):

Unmarshmaling json to nested struct

Casting interface{} to struct in json encoding

I attach you my go code: I want to extract each value

I don't know how I can get each value and to store it in a different variable like this:

music_type := ...
fmt.Println(music_type) // Rock

Can somebody help me please ?

Thank you!