Just like you would speak to any person.
I wish there was a more lengthy and fact filled answer, but that's really how it is.
Remember, just because you speak to them doesn't mean they will speak back, or that you will able to hear them. It helps to have a digital recorder or a very powerful microphone attached to a recording device while you are speaking to the entity, that way if there is a possibility of capturing anything you can.
yess of couse! you just speak whaleee
There is no definitive answer as ghosts are a supernatural concept and do not adhere to a specific language. In popular culture, ghostly communication is often portrayed as sounds or whispers rather than spoken language.
because they are durka durkas
The same way they survive without bones
If in England, America, or anywere that speeks english. They did used to be humans, after all.
read the bible
In the Odyssey, he did not go into the Underworld but merely summoned ghosts of the dead to speak to him.
it is suggested that animals including cats can sense ghosts or spirits , because they are sensetive. however cats cant speak english and are unlikely to be able to talk to a ghost.
Some of the oldest stories known to mankind already speak of ghosts, souls and "higher beings". If your question had been "since when do people talk about (...)" the answer would probably be: since they can speak. Your question, however, is "since when do they KNOW". Not about stories, but actually know about ghosts and souls. The answer to that question is: not yet. The first person to prove knowledge is still entitled to the one million dollar that James Randi has offered.
In your imagination. No one has discovered any other reliable way. In fact, no one has yet shown proof that they exist.
Some say when you are in a theda state, in between wakefullness and sleep, they can speak with us and may be heard as voices in our heads
No, belief in western type ghosts is not part of Buddhism. What some people, who are incidentally Buddhists, believe is of course up to them.Yes, many Buddhists would accept the idea of formless beings like ghosts.