1)
What is the significance of the names of the city?
1.
Rashi (Yehoshua 15:15): Kiryas Sefer refers to Halachos that were forgotten in the mourning over Moshe. 1 Osni'el ben Kenaz recovered them.
2.
Radak: In Persian, Sefer is called Devir.
3.
Malbim: The city was designated Kiryas Sefer, i.e. Talmidim gathered to learn the Sefer Torah, and there was a Yeshivah; Osni'el headed it.
1
Maharsha (Temurah 16a): Now the city was called "Devir" - Devarim (matters) about which there is debate about them. Earlier, it was Kiryas Sefer - there was no Safek about them.