In Frankenstein, what did the man ask the captain?
I'm assuming you're referring to the fourth letter from Robert Walton to his sister, in which he relates his first encounter with Victor Frankenstein:
On perceiving me, the stranger addressed me in English, although with a foreign accent. "Before I come on board your vessel," said he, "will you have the kindness to inform me whither you are bound?"
You may conceive my astonishment on hearing such a question addressed to me from a man on the brink of destruction, and to whom I should have supposed that my vessel would have been a resource which he would not have exchanged for the most precious wealth the earth can afford. I replied, however, that we were on a voyage of discovery towards the northern pole.
So, Victor asks Walton where his ship is headed before he agrees to come aboard. Walton is astonished, as one would imagine a man trapped on the Arctic ice would not question the destination of a savior vessel.
Of course, he is also shocked by the very situation. they have been traveling in the North for months, & Walton has continuously conveyed his loneliness and depression through his letters. Now, his crew miraculously finds another lone man on the ice, & it is with this man that Walton will find the companionship he so desperately craves.