What way of Hashem will become known?
Rashi: His Midah to benefit His nation.
Radak: It is all His ways - "Ki Mal'ah ha'Aretz De'ah Es Hashem" (Yeshayah 11:9).
Malbim: [After Hashem answered that the famine is due to the sin against the Giv'onim,] all knew that Hashem does Mishpat also for converts. (In particular, the answer was that the famine is because Sha'ul was not eulogized properly, and because he killed the Giv'onim. Chazal said about this, where His Mishpat is, His action. He held the pan of Mishpat on one side, and the pan of merit on the other side; these are His two ways - Chesed and Mishpat.
Why does it say "ba'Aretz" and "b'Chol Goyim"?
Radak: His way will be known in the land when all nations know His salvation.
Malbim: This is the opposite of Shamayim. I.e. also in the land they will know Your hidden ways, and all the nations will know Your salvation for all who rely on You.
