Everything turns on whose hand it was in: capacity and deliberate separation in your own, threat and sharp language in somebody else's.
Whatever else fades by breakfast, dreamers remember who was holding it, and that one detail splits the tradition down the middle. A knife in your own hand is taken as capacity: the ability to cut, to separate, to decide something that has been left joined together far too long. A knife in somebody else's hand is read as threat, and often as language rather than violence, since the oldest collections tie the blade to words meant to wound.
The favourable readings nearly all involve using the thing for what it is for. A kitchen knife slicing bread, a blade opening a parcel, a clean cut through rope: these are understood as separation done deliberately, and they turn up in people who are in the middle of ending something and have already made their minds up. A blunt knife carries the opposite reading and is a surprisingly frequent report, generally connected to trying to finish a job with tools that are not equal to it. A blade that simply will not cut has sat in dream collections for centuries as frustration made physical.
Being threatened with a blade, or being cut, is distressing to wake from and worth putting in proportion. The tradition reads the wound symbolically and does not treat it as information about your body or anybody else's, and it is not taken as a warning that anything is going to happen. Where a real person held the knife, careful readers say the same thing: the dream reflects your feeling about them, and a feeling is not evidence. Blood, if it featured, has its own long and largely non-literal set of readings.
Knives are also just objects that most people handle daily, and a cut finger on Tuesday explains a Wednesday dream better than any symbol will. Beyond that, what the object means to you is decisive. A chef, someone who was once threatened with one, and someone who simply finds them unpleasant to look at are three different dreamers, and only one of them is having the dream described above.


