As of my last knowledge update in September 2021, the forex market stands as the biggest and most liquid financial market globally, boasting an average daily trading volume surpassing $6 trillion.1
References
1Mahjouby ME, Manzali Y, Bennani MT, Lamrini M, Far ME. Machine Learning Technique to Predict the Right Buying and Selling for EUR_USD. International Journal of Intelligent Systems and Applications in Engineering. 12(16s):439-445. https://ijisae.org/index.php/IJISAE/article/view/4856