Halacha forbids speaking during the recitation of Shema or the Berachot preceding and following Shema. Is one allowed to interrupt during this recitation to answer "Amen" to a Beracha or Kaddish, or to respond to Barechu or Nakdishach?
One who hears Kaddish during Shema or the Berachot of Shema answers the first five "Amen" responses. This means that he may answer to all the responses of the half-Kaddish, but not to "Titkabal," "Al Yisrael," "Yeheh Shelama" or "Oseh Shalom." One may also answer the complete "Yeheh Shemeh Rabba" response, through the words, "Da’amiran Be’alma." This is in accordance with the view of the Arizal (Rabbi Yishak Luria, 1534-1572) that in this response one must recite the twenty-eight words from "Yeheh Shemeh" through "Da’amiran Be’alma." One may answer this entire response if he hears Kaddish while reciting Shema or the Berachot of Shema. This is the view of Ben Ish Hai (Rabbi Yosef Haim of Baghdad, 1833-1909) and the Kaf Ha’haim (Rabbi Yaakob Haim Sofer, 1870-1939).
One does not interrupt Shema or the Berachot before or after Shema to answer "Amen" to a Beracha that one hears. If, for example, a person reciting Shema or the Berachot of Shema hears the person next to him recite a Beracha, or he hears the Hazan recite the Beracha of "Yoser Ha’me’orot" or "Ha’boher Be’amo Yisrael," he should not answer "Amen."
There are, however, a number of exceptions to this rule. First, one who hears the introductory Beracha of Birkat Kohanim while reciting Shema or the Berachot of Shema may answer "Amen" to that Beracha. He may also answer "Amen" to the three blessings of Birkat Kohanim. The reason for this exception is that Birkat Kohanim may be recited only in the presence of Minyan, which reflects its status as a "Dabar She’bikdusha" (recitation expressing the sanctity of God). This special status warrants interrupting Shema or the Berachot of Shema for the purpose of responding.
By the same token, one may interrupt Shema or its Berachot to answer "Amen" to the Berachot recited over the synagogue Torah reading. This Torah reading requires the presence of a Minyan, and thus it, too, constitutes a "Dabar She’bikdusha." As such, one may interrupt Shema or its Berachot to answer "Amen" to the Berachot recited over the synagogue Torah reading.
Likewise, it is permissible to respond to "Barechu" while reciting "Shema" or its Berachot. One interrupts Shema to respond to Nakdishach, as well. However, this applies only to the crux of Kedusha – the verses of "Kadosh Kadosh" and "Baruch Kebod." One may not recite the other passages of Nakdishach while he recites Shema or its Berachot.
If a person hears the congregation recite "Modim De’rabbanan" as he recites Shema or its Berachot, he joins them for the recitation of the three words, "Modim Anahnu Lach."
If as a person recites this section of the prayer service the congregation removes the Torah from the ark, he does not join them for reciting "Berich Shemeh" or "Ve’zot Ha’Torah."
Finally, if one uses the restroom during the recitation of Shema or the Berachot of Shema, he should not recite Asher Yasar immediately upon leaving the restroom, as one normally does. Rather, he should wait until after the Amida and recite Asher Yasar at that point.
Summary: One who is reciting Shema or the Berachot before or after Shema may not speak, but he may answer the first five "Amen" responses of Kaddish (including "Yeheh Shemeh Rabba"), the verses "Kadosh" and "Baruch" in Nakdishach, Barechu, and "Amen" to Birkat Kohanim and the Berachot recited over the congregational Torah reading. He also recites the words "Modim Anahnu Lach" if he hears the congregation recite "Modim De’rabbanan."
