On the question of Buggy or Shanks knowing the location of Raftel and/or One Piece, it's unclear. Buggy has shown some aspiration to the title in the past. If he knew where it was, why didn't he go get it years ago, after Roger's execution at Loguetown? Perhaps he was still too weak. Likewise, if Shanks knows its whereabouts, why hasn't he already become Pirate King? Is it too troublesome to get around the other Emperors, or does he just not care about the title?
Furthermore, it was never stated how much time passed between Roger's landing at Raftel and his execution at Loguetown. It might have been a few days, or it could have been years. Both Buggy and Shanks looked fairly young during their apprenticeship to Roger, and not much older than their late teens at his execution (from Shanks' flashback).
According to Oda (SBS, Vol. 4) Shanks was 27 when he visited Luffy's village, ten years before the current story. Luffy was 7 at that time. Since the current story takes place 22 years after Gol D. Roger's execution, we can say that:
So, 12 years had passed for Shanks and Buggy since they parted ways for good. Just to re-check their ages back at Roger's execution:
Wow, they were even younger than I had thought! So, Roger's execution couldn't have happened very much after they began their apprenticeship, unless they were pre-teens when they joined. Given that Roger's title of Pirate King stemmed from his mastery of the most dangerous ocean on the OPlanet, I personally doubt that he just skipped into Raftel and then waltzed off to his execution. I am sure some time passed between those two events. When looking over all of this, I become more convinced that Shanks and Buggy were not with Roger when he landed on Raftel, but joined sometime afterward. Therefore, they would not necessarily know how to reach Raftel