1)
Why must he request that Hashem hear his voice?
1.
Malbim: He asks that He accept his prayer to fulfill his request.
2)
What is the grammatical form of "Kashuvos"?
1.
Radak: This is like "Shachulos" (Yirmeyah 18:21), the plural of "Shachulah" (Shir ha'Shirim 4:2).
3)
What is the meaning of "Tihyenah Aznecha Kashuvos l'Kol Tachanunai"?
1.
Malbim: Hearken to the quality of my supplications - my justified claims.