Who guided David to the Amalekites who had raided Ziklag?

Answer: An abandoned Egyptian slave

David's men found an Egyptian left behind sick by his Amalekite master, revived him with food, and he led them to the raiders.

“Now his men found an Egyptian in the field and brought him to David. They gave the man water to drink and food to eat—”— 1 Samuel 30:11 (BSB)