Responding "Amen" to the end of Kaddish

Hi,

The "Amen" response to the Half-Kaddish, and to the corresponding parts of the Whole Kaddish, is obligatory [such that one would do it even during psukei d'zimra]. The same is likely true for the Amen response to Titkabel in the Whole Kaddish.

The Amen response to the last two lines of the Whole Kaddish, though, is not obligatory, but only optional.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 3:101; he does not discuss the response to Al Yisrael)

Have a great day,
Mordechai