I was learning Torah in a room next door to the shul because I already davened in an earlier minyan, and I hear the Shliach Tzibbur say birkas hashachar, kedusha, chazaras of shmonei esrai and many kadishes. Do I have a requirement to answer Amen and stand for kedusha and kadish as if I were a part of the minyan or do we say osek bmitzva patur min hamitzva in this case because if I were to answer each time I heard amen I would not been able to concentrate in my learning? Would this din be any different if I were in the same room because sometimes I learn in the same room as the minyan as well,
thank you for all your help
You should stand up and answer Kedusha as usual. The main part of Kaddish should preferably be answered (amen yehei Shemei Rabbah, and the next amen), but you need not stand up for it. If answering amen for other brachos will disturb your concentration, you need not answer them.
Sources: See Divre David (no. 41) who writes that there is an obligation to respond to Kedushah, but not to regular Amen’s. Other authorities maintain that there is no obligation even concerning Kedushah (see She’arim Ha-Metzuyanim Behalacha 20:1), but the general custom is to respond to Kedushah, whereas others are stringent even with regard to regular Berachos (Eimek Teshuvah 1:1; Notrei Amen vol. II, p. 166). The compromise given in the answer is based on HaRav Shlomo Zalman Auerbach zt”l (Halichos Shlomo 9:6) and Shevet Ha-Levi (9:43).