What did Yehoshua speak then?
Rashi: When the sun runs its course, it sings Shirah. Now that Yehoshua told it to stop, he sang in place of it.
Radak, citing Targum Yonasan: Yehoshua praised. (a) Perhaps his Shirah (praise) was after his Tefilah; the Navi does not record his Shirah. Or, the Shirah was "va'Yidom ha'Shemesh
What was "l'Einei Yisrael"?
Radak #1: The sun should stop in view of Yisrael.
Radak #2, Malbim: He said this prayer (that the sun should stop) aloud, in front of Yisrael.
What is the meaning of "Dom"?
Rashi #1 (from Tanchuma Acharei Mos 9): It is to be silent. When the sun runs its course, it sings Shirah.
Yisrael already defeated the enemy. Why did Yehoshua request this miracle?
Malbim: Moshe requested "Yelech Na Hashem b'Kirbeinu" (Shemos 34:9), that the Shechinah should cling with us without intermediaries. The war would not be natural via an angel, rather, miraculous. Hashem granted this. Yisrael will be distinguished in three ways. (a) He will do wonders for us, exposed and known to the entire nation - "Neged Kol Amcha E'eseh Nifla'os" (34:10). (b) They will be wonders without parallel until now
Where is Emek Ayalon?
Rashi: It is far from Giv'on, for Giv'on is within the border of Binyamin (which was next to Yehudah, which was in the south), and Ayalon is in Dan, in the north 1 .
Why did he tell also the moon to stop?
Radak: Yisrael chased the enemy from Giv'on to Ayalon. When the sun set, they were in Ayalon. This was at the beginning of the month, when the moon illuminates at the beginning of the night. It was still until Yisrael finished taking vengeance against its enemies (verse 13).
Metzudas David: Perhaps he was concerned lest the moon pass in front of where the sun was stationary, and block its light.
Malbim: It is a greater miracle that the Galgal (spherical shell that houses the Heavenly bodies, which rotates daily) continue to rotate, but the sun and moon stop, than for the Galgal to stop. 1
Malbim: It takes more strength to hold back a water mill from grinding when the water flows on it, than to cut off the flow of water.