Where is a worm hole situated?
The first thing to understand is where worm holes come from. In the early part of the last century, Albert Einstein published a paper on General Relativity (GR) describing a new way to explain gravity. Instead of thinking of gravity as a force between objects with mass he described it in terms of geometry that is not flat and whose curvature depends on the local mass energy. Space can also have a more general curvature described the Cosmological constant - Wikipedia. Out of this theory came some equations. One of the possible but unusual solutions of these equations is the well known black hole. At the time this solution was found it was not known if such an object existed. Later observations found evidence that there are such objects. Today black holes are accepted as a real and important part of our universe.
Another possible solution to these equations is a worm hole. This is a direct passageway between two locations in space time. Like black holes in the 1930's, it is not known if worm holes exist in the universe. All that is known is that their existence is not in contradiction to GR. There's a notion (not a theory fact or law) that anything allowed, must be.
There are reasons to suspect that worm holes don't exist even if they could. If they do exist it is unlikely that they would be useful the way they are used in science fiction, to allow someone to traverse large distances quickly, or even used to communication. One argument against worm holes goes like this.
A worm hole could let you travel to a moment in the past. This would allow paradoxes such as the Grandfather paradox - Wikipedia and therefore they are not possible.