Without looking into any sefer, answer the following questions (you can check yourself after you have answered):
During krias Shema and its blessings, is one permitted to interrupt for…
1) Kaddish (if yes, which parts of it?)
3) Kedusha (if yes, which parts?)
4) Amen (if yes, which Amens)?
5) Baruch Hu Uvaruch Shemo?
6) what to do if one is called by name for an aliyah?
7) what to do if one hears thunder or lightning?
During Pesukei D’Zimra…
answer 1 – 7 above
During Elokai Netzor…
A. 1-3 I think yes, 4-7 I think no
B. The same
C. 1-5 yes, 6-7 no
During krias Shema and its blessings, one interrupts to answer Kaddish [Amein, Yehay shmay rabbo…. and the Amein after “Bruch hu” (in Nusach Ashkenaz)].
One also interrupts to answer Barechu and Kedusha (for sure, he should say “Kadosh Kadosh Kadosh…” and “Baruch kevod…”). As far as Yimloch is concerned, the standard psak is not to say it; however, the minhag in Chabad is that one does say Yimloch, as well (this is based on the ruling of the Arizal).
4) Not quite. One answers Amein to the blessings of “hakel ha-kadosh” and “shomea tefilla,” as well as the blessings said by a person who received an aliyah, as well as the blessings said by the person who read the haftorah, as well as the blessing said by the Kohanim when they begin blessing the congregation.
5) Do not respond
6) He should go up, but not read along. Ideally, get to the end of the paragraph before going up, but if not, it’s also OK.
7) Machlokes haposkim. R’ Akiva Eiger, the M’kor Chaim L’Chavas Yair, S’U Keren L’Dovid say to make the bracha, while Chayei Odom, Elya Rabbah, Likutei Maharich advise against it.
B. During Pesukei D’zimra, one may interrupt to respond Amein to any bracha, since Amein is also a praise.
He can say the full Kedusha (although Rabbi Eli Mansour shlit”a allows answering only “Kadosh…” and “Baruch….”
Some permit him to read along with the baal koreh if he was called for an aliyah while reciting Pesukei D’Zimra.
C. Elokai Netzor has exactly the same halachos as krias shema and its blessings. The Kitzur Shulchan Aruch and the Ben Ish Chai allow interrupting to respond Amein to any bracha at this point in davening, since S”E is already over and one is only making additional supplications. However, the standard psak is not to do this, though I would imagine that if one really wants to, he could.
Regarding a person who is holding in krias shema or its blessings, when the tzibbur is up to Birkas Kohanim, the question is, whether he can say Amein…
I saw in one source that he should say Amein to the verses but not to the bracha. However, Piskei Teshuvos 66:6 says that one should interrupt the birchos Krias Shema as well as Krias Shema itself (except if one is in middle of the 1st Possuk of Shema w/Boruch Shem Kivod etc.) to answer Amein to the beracha made by the Kohanim when they begin blessing the congregation.