I'm in Piano grade 7 Royal Conservatory of Music and I'm finding Analysis to be quite challenging. I have no problem reading the music but if I really want to be able to learn a piece well I have to learn how to analyze pieces and keep in mind or the underlying harmony. The thing is, I can't really figure out the underlying harmony because I can't do things like distinguishing between chord tones and non-chord tones and with modulations. does anyone have suggestions on books, videos, guides on harmonic analysis and some good pieces to start practicing with?
I know how expensive textbooks are, but I genuinely think a great textbook is the best answer to your question. Probably my favorite textbook for straightforward learning outside of a class environment is the text by Aldwell and Schachter called Harmony and Voice Leading. However, it's probably the most difficult standard text and might be better after you've already learned some details from elsewhere. A somewhat simpler, but still great, textbook is Clendinning and Marvin's Musician's Guide to Theory and Analysis.
As far as some pieces that are somewhat easier to do an analysis of due to relative lack of non-chord tones and chromaticism, you might try the beginnings of Bach's first prelude from the first book of the Well-Tempered Clavier and Beethoven's so-called Moonlight Sonata, but even those will have the occasional moment that takes further study to understand.
As a Royal Conservatory of Music graduate, I'm sorry I need to say this, but have you ever taken Harmony lessons? Basic Harmony (2009 syllabus) and Level 9 Harmony (2016 syllabus) both teach non-chord tones.
In addition, the 2009 syllabus has a list of resources (books) you can draw upon for music theory lessons.