Making people forget the name of the Israelites represents making them forget the Israelites. In this case they would do it by killing the Israelites. Alternate translation: "They will surround us and kill us, and the people of the earth will forget about us" (See: [[rc://en/ta/man/jit/figs-metonymy]] and [[rc://en/ta/man/jit/figs-explicit]])
The phrase "your great name" here represents God's reputation and power. Alternate translation: "And so what will you do so that people will know that you are great" (See: [[rc://en/ta/man/jit/figs-metonymy]])
Joshua uses this question to warn God that if the Israelites are destroyed, then the other people will think that God is not great. Alternate translation: "Then there will be nothing you can do for your great name." or "Then people will not know that you are great." (See: [[rc://en/ta/man/jit/figs-rquestion]] and [[rc://en/ta/man/jit/figs-explicit]])