It is worth 3 betting light when we have a position, with hands that we don't want to call, as we don't hit the flop well. Like, Ax, Kx, Qx, Jx ..?

If you have enough stack, and are in position, 3 bet the hands you mentioned. A high card, without a connector, or kicker, does play. Making top pair is a good position, but precarious, without a kicker or draw.