coffins withDracula lying inside one:  "There lay the Count, but looking as if his youth had been half renewed . . . on the lips were gouts of fresh blood, which trickled from the corners of the mouth and ran over the chin and neck. . . He lay like a filthy leech, exhausted with his repletion."  Jonathan, terrified, closes the coffin lid.  Shortly after this, Dracula's body is transported to England, Jonathan escapes, and then of course goes mad.  I would think finding Dracula in the coffin confirms Jonathan's knowledge, even though he does not use the word "vampire."  Only later does the doctor introduce that term.  However, Jonathan does call the Count a "monster."

In one entry in Harker's diary prior to his discovery of the Count in his box, it occurs to him that he has "not yet seen the Count in daylight." This leads him to wonder whether he actually sleeps at night, and Harker decides he must seek out where the Count sleeps and try to get into his room.

In the next entry, Harker recounts how he "made the effort" and escaped back to his own room unscathed. Taking off his boots, he climbed out of his own bedroom window and in through the Count's but found the room entry. Venturing through a "heavy door" in the corner of the room, he then descended down a dark passage, out of which came "the odour of old earth newly turned." Proceeding still further into the vaults, Harker found a pile of "great boxes" on a pile of "newly dug earth." In one of these lay the Count, "either dead or asleep," with his eyes open and yet not having the appearance of death.