In which parts of China or Asia can you find Hokkien speakers? Also, where can you learn Hokkien Chinese?
Though Hokkien = 福建 or Fujian，a southeast coastal province facing Taiwan. Hokkien Chinese actually means 闽南语 which is originated from south part of 福建, and also commonly used in Taiwan Island, Southeast Asia and many other Chinese societies overseas.
In fact people living in north part of Fujian speak a totally different dialect, which is almost not understandable to Hokkien-speaking Chinese.
Hokkien is spoken by around 50 million people. About half are in Fujian province (i.e. "Hokkien" province), mainly around the cities of Zhangzhou (Chiang-chiu), Amoy (Ē͘-mûi/Ē-mn̂g), and Quanzhou (Choâⁿ-chiu) -- not all of Fujian province. The other half are spread across South-East Asia, descending from settlers who left Fujian in the 17th and 18th centuries. This includes most of Taiwan, as well as communities in the Philippines, Malaysia, Singapore, and Indonesia.
Outside of these areas, it can be difficult to find somewhere to learn Hokkien. The most well-supported variety of Hokkien is probably Taiwanese Hokkien (often simply called "Taiwanese"). For example, there is a textbook called "Southern Hokkien: An Introduction", by Bernhard Fuehrer and Yang Hsiu-fang, which focuses on Taiwanese Hokkien. This is used by a course taught at SOAS (School of Oriental and African Studies) in London.