Retired English Teacher
1. He's planning to go on a one-week trip in Hawaii.
2. He's planning to go on a one-week trip to Hawaii.
Which one is correct? Are they both correct? Thank you.
It depends on the context.
In #2, I would think that the person lives elsewhere and is planning a one-week stay in Hawaii.
I don't think #1 sounds very natural, though you might say that "he is planning a one-week trip while in Hawaii." This would imply that his stay in Hawaii will be longer than a week.