How did Han know?

@MeadowofAshes

I was thinking that maybe there're three group of Force Sensitive people, where Group 1 will be the majority who have their Force Signal easily pick up by other Force Sensitive and usually trained to be Jedi or Sith with basic skills. The second Group would be people like Han, who most of their life did not aware of their power since it's hard to notice by common or inexperienced Jedi/Sith and for those people, they considered it as pure luck due to their Force Power being on a subconscious level, can't be seen or observed(like Professor X or Jean Grey). And the Last Group would be those who Are the combination from Group 1 and 2 where these few individuals can be extremely powerful and strong in the Force, they can do any Jedi/Sith basic skills as well as able to do some higher, more advanced skills, Jedi Mind Tricks, etc.

But since Group 2 is so hard to find and notice, most Jedi and Sith alike did not aware of their existence or that Group 2 people Force Power is hard or weak to be training as other normal, common Force Sensitive people. Not to mention, they could just put Group 1 and 3 together since "they are all Force Sensitive". In TNH, maybe Obi Wan, after all those year training in the Force, had realized that Han is in fact a Group 2 Force Sensitive.

I think Finn is too.

@motherofpearl1

Yes, I think Finn would be in " Group 2" along with Han. Though this is just my speculation since there's no hard evidence for this

Not to mention people like Leia who have potential in the Force but choose not to use it. Personally I would said that they can be considered in "Group 2" as well