Knowing is a loosely defined term. Therefore there could be many answers to this.

We know that babies start to form useful knowledge when they are three to four months old. This implies that knowledge is acquired by learning after birth.

Unconditioned reflex is an unlearned reaction toward a stimulus. If reflex counts as knowing, then human has a lot of them even just after they are born. Those reflexes are primitive reflexes and many of them are there even before the baby is born. However, these reflexes will go away once the frontal lobes of the brain undergo development. Doctors use those reflexes to evaluate the baby's nervous system.

The following are some interesting primitive reflexes:

Swimming reflex: An infant up to 4 or 6 months old can hold their breath and swim when they are submerged under water.

Grasp reflex: An infant up to 6 months old can grasp any object placed in their hand.

Stepping reflex: An infant up to 6 months old will put one foot in front of the other if their sole is placed onto a flat surface, although they cannot support their own weight at that point.