Light travels as far as it is allowed to, which is to say that it travels until it interacts with something. For instance, sunlight -- a form of light -- that comes from the sun at the Earth travels in space until it hits the Earth's atmosphere, where some of the sunlight goes into the gas in the atmosphere and some of the light is reflected. The light that goes through hits different things on the Earth's surface. In some cases, the light turns into heat and warms things up; in some cases, the light is absorbed into plants as energy. If these things did not exist, the light would keep traveling until it hits something else.

The short answer is that light will travel as far as it can, and we cannot predict how far it travels unless we know what it might encounter as it travels.

Theoretically, light can travel infinite distances. However, because the universe is only 13.7 billion years old, light has only been able to travel 13.7 billion light years, so we can't see anything more than 13.7 billion light years away, and even then we see it as it was 13.7 billion years ago, not as it is now.

Additionally, because the space of the universe is expanding, however, there is a limit to how distant an object that light can reach - the space beyond that distance is moving away from us faster than the speed of light, such that light can no longer reach it (note: nothing in space can move faster than light, but space itself is not subject to this limitation).