Is there any music theory for classical guitar learner? Most of the books I've read focus just on note reading and chord, scale in a visualized way, not on the relations between the musical stuffs.
Please suggest me,
This is a common misconception but there is no specific theory you learn for each instrument, you can learn the ABRSM theory books regardless of what instrument you play.
Granted the application of the theory you learn is specific to your instrument but for the most part, the G Major scale is the same regardless of instruments.
Your profile does not say where you are from but for a general idea, you could get a teacher to teach you the ABRSM method. It is more than adequate for guitarists.