It in the weapon stat block of the character sheet.
There's Range/Reach, Grip, Size, Damage, Loads, and Qualities.
I know what all the others are, and I thought grip might be one handed or two handed, but in the rulebook 1H and 2H are listed as sizes.
Unbalanced is conditional based on Brawn, so I thought maybe grip was there to remind the player if it's 1H or 2H for them, but I wasn't sure.
There's also no rule about using a 1H weapon with two hands (or a rule prohibiting it), so I thought maybe Grip would be to remind the player how they are holding the weapon since disarm's cost is based on the weapon being 1 or 2H.
I also thought Grip might have been a hold over from an earlier draft and the inked character sheet was too cool to throw out.
I asked the same question to Lloyd Gyan last summer. His first answer was the same as you (1h/2h). I didn't make sense to me because there's is a "Size" box. That's what the rules refers as 1 handed or two handed.
He came back later with that answer:
Grip is an extra set of rules that will be released later for Advanced Two handed weapon rulings, as there was a lot of feedback that people who do so are shafted.