Which grain is discussed?
Radak: It is the grain of the 25,000 Kanim.
It is written with a Hei, and we pronounce it "Tevu'aso"!
Radak #1: Refer to 48:8:3:1.
Radak #2: The Hei at the end of the word is in place of a Vov, like "Ohalo" (Bereishis 9:21). The same applies to b'Socho (above 8, 15).
Who are "Ovedei ha'Ir"?
Rashi citing Menachem: They are the Giv'onim 1 , who were given to cut wood and draw water [for needs of the Mikdash].
Radak: It is those who dwell in the city. There will be people from every Shevet. They will do the work of the city in fields, vineyards and gardens.
Malbim: They are those who engage in the work of the city.
Radak (19): This is wrong. The Giv'onim will not serve in the future. It cannot be that they will dwell in Yerushalayim, the Kadosh city, for the sake of Yisrael!