The "unknowns" you mention are scattered throughout "The Most Dangerous Game" by Richard Connell, and they are certainly not limited to this list.
The unknowns begin while Rainsford is still on the ship.
- He sees a mysterious island through the fog but does not know exactly what makes him "feel something like a sudden chill."
- As they pass the island in the dark, he hears the unexpected sound of gunshots. "Somewhere, off in the blackness, someone had fired a gun three times," but he does not know who shot what.
- When he falls overboard, Rainsford is in the water and an eerie sound "came out of the darkness, a high screaming sound, the sound of an animal in an extremity of anguish and terror." He is unable to identify the animal, even though he is a hunter and has hunted every known animal.
- He finds a gun cartridge once he lands on the island and is surprised at the small caliber, which would not have been strong enough to kill a large animal like the one he heard the night before.
- He sees a castle-like mansion in the middle of this deserted island.
- Everything about General Zaroff suggests he is a man of great refinement, yet there is something Rainsford does not know at first--that Zaroff hunts humans and Rainsford is his next game. Zaroff says he is only interested in hunting animals that
"have courage, cunning, and, above all..., must be able to reason."'
"But no animal can reason," objected Rainsford.
"My dear fellow," said the general, "there is one that can."
- Rainsford is offered a choice: be hunted or be turned over to I Ivan (the Cossack). He does not know exactly what Ivan will do, but he suspects the cruelties Ivan is capable of and chooses to hunt.
- When Rainsford is being hunted by Zaroff, he discovers many things he does not know about this island and about the General's hunting techniques.
The final two unknowns happen at the end of the story. First, Rainsford is trapped.
Twenty feet below him the sea rumbled and hissed. Rainsford hesitated. He heard the hounds. Then he leaped far out into the sea. . . .
Though he does not know if he will survive the jump, he knows he will be killed if he stays where he is. Second, he does not know for certain that he will be able to defeat Zaroff once he does make his way back to the chateau; however, he is willing to fight and do his best to keep Zaroff from hunting any more humans.
Nearly all of these "unknowns" are foreshadowings of what is to come, if only Rainsford had been able to recognize what he was seeing and hearing. It is also interesting to compare the arrogance Rainsford displayed concerning the feelings of the hunted at the beginning of the story to his feelings about being hunted at the end of it.