I know this "knowing" feeling quite well. I have had two especially vivid experiences that I will never forget.
One was while sitting in a Starbucks in Edinburgh, Scotland, a few years ago.
It was a cloudy, nippy day in February, and I remember distinctly the coziness I felt and the wonderful atmosphere----hot chocolate at my elbow, soft jazz playing, warm red and golden hues in the room, and a huge bay window across from me, providing a stunning vista of the Edinburgh Castle. I was there all afternoon, studying.
But what made the experience especially memorable was a young man who sat only a couple chairs away from me at the same table. (It was a big table, one that could seat about six or so people.) Anyway, this young man, a dark-haired, good-looking fellow, sat near me, and stayed with me at the same table the whole afternoon. Everyone else sitting at the table eventually left, just leaving the two of us alone. We never said a word to each other, but something about his presence was immensely comforting, and I felt as if we knew each other somehow. I couldn't explain it at all.
Even without words, even though we were complete strangers, I felt as if our souls were connected in some way. But maybe it was just because were fellow partakers of a magical afternoon in a Starbucks in Edinburgh. And it only became more magical when the view outside the big bay window turned into a literal "snow globe." The castle was soon nearly obscured by a driving flurry of white. However, the magic of everything couldn't prevent my sleepiness, and so I put my head down and took a brief nap....when I awoke, my "friend" had vanished. Sometimes I wonder if he was an angel.
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The other experience I had was somewhat similar to Hema's story. I used to work at a salad bar, and one night while I was working, this elderly couple and two little children, who I assume were their grandchildren, came to get some salad. What struck me immediately about this couple and the children was the joy they seemed to possess. They were laughing together, and seemed so full of genuine happiness.
Then, as I'm standing there, observing them discreetly while I continue my work, the little boy, who couldn't have been more than 6 or 7 years old, suddenly turns to look up at me. I will never, for as long as I live, forget the way he looked at me. He smiled in the most tender way at me, and his big, beautiful, blue eyes just latched onto mine. I felt as if he were looking straight through me. I felt, all at once, with that brief stare, that he knew everything about me, that he could see into my soul, and yet was smiling up at me in love and compassion. It just left me stunned for a while. I was going through a rough patch in my life at that point, and it was like God comforted my heart through that little boy. When I looked into his eyes, I felt I encountered God.
I really and truly wonder sometimes if certain people we encounter are actually angels. And maybe that is why, at least in my case, I often feel as if I know, or am known, by complete strangers.