My boss is curious how much Modern Korean he can recognize from his fluency in Cantonese and Mandarin. He plans to start by learning solely Hanja, obviously to take advantage of his fluent Cantonese and Mandarin. We are referring just to Hanja commonly used by ordinary Koreans in 2021. We don't need archaic or esoteric Hanja that ordinary Koreans won't recognize.
We know that mastering Hanja is NOT enough to learn Korean, because Hanja constitutes just 60% of Modern Korean vocabulary. My boss is computer illiterate and asked me to post this. As his first choice, he prefers print books or monographs in English or Chinese. But if there are none, he can try trustworthy websites.