Strictly speaking there are no "JAV positions" as these positions are basically universal. But I'll mention my two favorites here. Both are variants of doggy, which is my favorite type of general position.
First is standing doggy, where the girl is bent 90 degrees, and the guy is holding her by the arms. This is done frequently in JAV, but infrequently in western porn.
Second is girl is on the floor, head and arms pressed to the floor, but on her knees while ass is straight up in the air, and the guy will penetrate almost vertically downwards. This one is common in western and uncommon in JAV. It's especially good for anal.