If you’re interested in learning Gann, you should read the books he authored and the books he suggested you study for background knowledge.
Books Gann Authored
Truth of the Stock Tape and the Wall Street Stock Selector (1923)
Tunnel Thru the Air (1927)
Wall Street Stock Selector (1930)
Fact Facts America, Looking Ahead to 1950 (1940)
45 Years in Wall Street and the New Stock Trend Detector (1949)
The Magic Word (1950)
How to Make Profits in Commodities
How to Make Profits Trading in Puts and Calls
New Stock Trend Detector
Scientific Stock Forecasting or Large Profits on Small Risks
Companion to Truth of the Stock Tape
Gann Commodity Course
Gann Stock Market Course
NUMEROLOGY
Numerology: Clifford W. Cheasley,
Philosophy of Numbers: Mrs. L. Dow Balliett,
Number Vibration in Questions and Answers: Mrs. L. Dow Balliett
The Day of Wisdom according to Number Vibration – Mrs. L. Dow Balliett
The Kabala of Numbers: “Sepharial” [How and Why Numbers Work]
How to Play the Races and Win: Mark Mellen
The Kabala of Numbers: Sepharial (Interpretation)
The Mysteries of Sound and Number: Sheikh Habeeb Ahmed
Numerology for Everybody
The Tarot of the Bohemians: Papus (Dr. Gerard Encausse)
The Power of Numbers: Numero,
Numerology Made Plain: Ariel Yvon Taylor
ASTROLOGICAL
Horary Astrology: Robert DeLuce
World Book of the Ages from Adam to the Millennium: H. J. Kerns
Raphael’s Pythones of the East: Raphael (Robert C. Smith)
Raphael’s Book of Dreams: Raphael
Raphael’s Mundane Astrology: Raphael
Zodiac and Bible: Fannie Muller
Mars – The War Lord: Alan Leo (William Fredrick Allen)
Ogilvie’s Astrological Birthday Book: Leo Bernart
Sepharial’s Astrology: Sepharial (Walter Gorn Old)
Astrology Explained: Sepharial
Astrology, Its Techniques and Ethics: C. A. Q. Libra
Key to the Bible and Heaven: Ludwig H. Larsen
Sciences and Key of Life: Alvidas (Henry Clay Hodges)
The Wheel of Life or Scientific Astrology: Maurice Weymss
Raphael’s Book of Fate: Raphael
Guide to Astrology: Fred White
Law of Values: Sepharial (Walter Gorn Old)
The Silver Key: Sepharial
Fortunate Hours: A. E. Partridge
Directional Astrology: Sepharial
The Stars: How and Where They Influence: L Edward Johndro
The Earth in the Heavens: Ruling Degrees of Cities: L Edward Johndro
Rectification of the Horoscope: Robert DeLuce
Astrology for All: Alan Leo (William Fredrick Allen)
The Secret of the Ages: Robert Collier
The Science of Foreknowledge: Sepharial (Walter Gorn Old)
The Astrological Ready Reckoner and Student’s Assistant: Sepharial
Your Stars and Destiny: Paul Councel
Manual of Astrology: Sepharial (Walter Gorn Old),
Textbook of Astrology: A. J. Pearce (Alfred John Pearce)(Old/Rare)
The Witness of the Stars: E. W. Bullinger
Solar Biology: Hiram E. Butler,
Cosmic Symbolism: Sepharial (Walter Gorn Old)
Popular Astronomy: Flammarion and Gore
Eclipses in Theory and Practice: Sepharial (Walter Gorn Old)
Sun Spots and Weather: W. T. Foster
Popular Astrology for Everybody: Frederick Hathaway
SCIENTIFIC AND MISCELLANEOUS
The Candle of Vision: A. E. (George William Russell)
The Path to Wisdom: Richard Lynch
The Doctor Prescribes Colors: Edward Podolsky, M. D.
Cosmic Causation in Geophysics: Paul Councel
The Master Key of Destiny: Gregorius
Evolution and Reincarnation: Essie M. Ducquan
Miracle of the Ages: Worth Smith
The Kybalion: Three Initiates
Sixth and Seventh Books of Moses
Mysteries Unveiled: William A. Redding
Peace and Relaxation through Technique and Truth: Henry Cooper
Faith as a Constructive Force: Swami Paramananda,
Oracles of Nostradamus: Charles A. Ward
The Sickle: William E. Walter
Lessons in Truth: H. Emilie Cady
Secret: Wesley W. Stout
Open the Door: Wilfred Brandon
The Proofs of Astral Influence on Man: Paul Choisnard
Spiritual Radio: Archbishop Du Vernet
Yoga System of Study – Occult Chemistry: Yoga Hari Rama
The Law of Psychic Phenomena: Thomson Jay Hudson
Power of Will: Frank Channing Haddock, M. S. Ph. D.
Oahspe: Dr. John Ballou Newbrough
Philosophy of Natural Magic: Henry Cornelius Agrippa
The World Book of the Ages from Adam to the Millennium: E. J. Kerns
Bible Mystery and Bible Meaning: T. Troward
God-Man: The Word Made Flesh: George W. Carey and Inez Eudora Parry
Tertium Organum: P. D. Ouspensky
The Chemistry and Wonders of the Human Body: Dr. George W. Carey
The World’s Greatest Thought Discovery: Mack Stauffer
The Goal of Creation: Edmund Shaftesbury
Most of them a freely available here