When did Eli give this Brachah?
Rashi: He gave it every year.
What is the essence of the Brachah?
Rashi (from Midrash Shmuel 6:3): All [future] children you will have, should be from this Tzadekes. (The words of the verse must be rearranged.)
Targum Yonasan: They will have [more] Kosher (proper) children from Chanah, in place of Shmuel.
Radak: You should have more children that will be with you, and serve you in your old age, in place of Shmuel, whom you gave to Hashem.
What is "ha'She'elah Asher Sha'al la'Shem"?
Radak #1: Each of them (Elkanah and Chanah) asked [for a son] from Hashem.
Radak #2: Both of them gave (lent) Shmuel to Hashem.
Why does it say "li'Mkomo" (singular)?
Radak: Ramah was Elkanah's place, but not Chanah's. She was from a family in a different city.
