Draw a node tagged with emergency=defibrillator as close as possible to the actual location of the defibrillator. If the location is not exactly known (for instance it’s know that a shopping mall has a defibrillator somewhere in the building, but not exactly where), place the node at a location where it is most likely to be (near an entrance or at an information desk, for instance) and add a fixme tag such as fixme=approximate location, needs survey. For higher attention, a Note can also be placed nearby asking for a survey. Do not add emergency=defibrillator to a building, amenity, etc. as this strictly means that the building is a defibrillator. It has been suggested that defibrillator=yes could be added to the building/amenity instead.
Placing a defibrillator at a non-exact location is a practice that should be resolved as soon as possible, so placing a note should be encouraged. Quickly finding a defibrillator can be a matter of life or death, so it is important to consider if adding a non-exact node is better than nothing (at least it’s known that there is an AED somewhere, so it can be searched for) or worse than nothing (looking for the AED at the wrong location may lead to not finding it at the actual location). The presence of a non-exact node also makes it easier for survey tools like StreetComplete to move it to the right location.