Neither got hit directly. If you go back and look at previous TBs Oda always places the user in the foreground of the panel, see Yamato and both of Kaidos, the reason is that in all of those instances the attack landed directly, meaning the club physically made contact with the victim, this is also supported by the fact that there is always a focus on the club itself in those panels, since it's drawn nearest to the viewer. When analyzing this particular incident we see that Oda didn't illustrate the TB in that manner rather he chose to draw two light streaks, one being Kaidos club itself and the other being the AdvCoC black lining. Funnily enough the black streak is the only thing that dispersed in that panel signifying that it made contact with both Zoro and Law equally, only the AdvCoC "force" not the club. Furthermore if we look at the positioning of all three involved you notice that Zoro was at a vertical to Kaido and Law was at a horizontal to Zoro; the vertical distance between Zoro and Kaido never actually changed, Kaido just moved horizontally and remained at the same vertical, which isn't enough distance for the Club to hit either of them. If we were to believe the scenario in which the attack hit then we would be agreeing that both a heavily injured Zoro and a tired Law have superior durability and endurance to a fresh boundman Luffy.....of course this is impossible. The final reason it doesn't make sense is because we see Law actually block the attack, an attack can't hit someone directly(to the body) and also be blocked, the only explanation is that it passed through his guard, which is only every indicated by showing damage being done to the tool one is blocking with, whether it be breaking or disarming. So our conclusion is that part of the AdvCoC "force" is the only thing that hit them which Law blocked with his sword but still felt the impact of and not the club itself, since if it did than it would be two opposing forces and objects colliding, thus if one overpowers the other it pushes it back; Law was not flung a great distance which would have been the case if he was trying to stop the club and counteract the force of the swing. Kaido would have hit Law like a baseball, home run.