1)
If the "Ish" was a stranger to Yosef, why did it suffice for Yosef to say "my brothers"? And why did Yosef expect him to know where they are?
1.
Ha'amek Davar #1 (to 37:15): Yosef was known to them to be important (so they would know also his brothers).
2.
Mizrachi, Ha'amek Davar #2 (to 37:15): Yosef recognized that he is an angel or Navi.
3.
Ohr ha'Chayim: "Leimor Mah Tevakesh" (37:15) implies that he asks him what he seeks.
4.
Malbim: Usually, shepherds go from pasture to pasture. They do not go far away.
