According to Fandom Wiki about Ging Freecss,
Genius-Level Intellect: Ging is arguably one of the most intelligent characters of the series. He has foreseen most of Gon's choices and actions since leaving home, including his participation in the Hunter Exam, his journey to Greed Island and his meeting with Kite. He also guessed correctly what the process to decide the rules of the election would be and ensured his own would win, outmaneuvering the rest of the Zodiacs. His predictions regarding the election for the new chairman of the Hunter Association were accurate and even Cheadle, despite disliking him and being extremely smart herself, asked him for advice. He manipulated Leorio, a person he knew nothing of, so that he could become a hindrance to Pariston's victory, which he did. Furthermore, when Ging got rid of the Nen users from Muherr's party at the underground level and was going back up to the castle, he pointed out to Pariston that if he wants to see his abilities he has to come at him rather than building up badly designed self-serving scenarios, showing his superiority as a battle analyst even in times of conflict. It can be affirmed that Ging's preeminent mental skills are his deductive intelligence, quickness of mind and versatility. Ging is a polymath since he has extensive knowledge in various fields of academic studies. However, he claims that he studies subjects that interest him only.
Ging is also able to correctly guess someone's natural Nen type the instant after they had used an ability, as he did with Muherr's henchmen, which implies he may have learned or developed his own system to identify different Nen users; though he was unable to identify the guns as not being conjured by the henchmen themselves. Ging's knowledge in Nen also allows him to identify Golem as a symbiotic Nen user upon the first impression.
I am sure he knows the Nen abilities of Gon as well.