Does a cat know when another cat in the house dies?

It's possible, however it is unlikely to happen because it can be affected by many things and we can't just tell it to the cat. for example if one cat manages to leave the house and has an accident outside, the other cat will not understand and will just keep waiting for the one cat to come back. If the second cat actually sees the first cat dead and he/she might understand but then again he will not understand why or how it happened. It's hard for people to understand animals but if the owner knows the cat well enough he/she can notice cat's mood and behaviour changes.