There are many completely impractical, but at the same time extremely entertaining questions. This question is just one of them. Let’s deal with.
Since all people are distributed over the ground more or less evenly, nothing will happen in general, since the blows from landing of people at different parts of the Earth mutually compensate for each other.
Yes, of course, if we consider the land like a ball, it turns out that almost for all sites of sushi on the other side of the earth is the ocean. Only Portugal is slightly intersect with New Zealand. Also in the northern hemisphere, much more people than in southern, but still, since the effort will be smeared along a large surface. A significant part of it is mutually compensated and the resulting force will be negligible.
Let’s imagine that some kind of magical way all people gathered in one place. For simplicity, we assume that all people jump on the same height — 30 centimeters.
On Earth about 7 billion people. The total mass of all people can be estimated at about 400 billion kilograms. Earth weight is equal to 5.97 • 10² ⁴ kilogram. It is approximately 12,817,518,248,175 times more mass of all people on Earth.
The mass drop in 400 billion kilograms will cause a change in the rate of the Earth’s orbital movement by about 2.6 • 10⁻⁻³ m / c. In other words, it is from the Earth’s orbit shift by about 0.25 nanometers or about half the diameter of the hydrogen atom.
However, the Earth will very quickly «bounce» back due to the gravitational connection with the Sun.
More interesting effects can be on the site of such a jump. If we assume that all people will gather together on a relatively small territory, for example, in the territory of such a city, like Moscow and the entire jumping surface will be asphalted, the joint landing of all people will cause the strongest noise, an acoustic blow that is comparable in volume with an atomic bomb explosion.
It will also cause a very strong earthquake in this area. The exact force of the earthquake is difficult to predict, but most likely it will be one of the strongest earthquakes in history.