If one is davening Shmone esrei in a minyan and finishes only after the shaliach tzibbur has already begun tachanun, for which parts does one pause in kedusha, kaddish (if no tachanun-eg. ma’ariv), and tachanun (13 midot)? Same question for responses permitted during "Elokai Netzor Leshoni..."?

If, while you are in the middle of “shmone esrai”, you hear the chazan saying kaddish, kedushah or barchu- you should pause in silence to listen with the intent of participating- by listening- with what is being said. By “kaddish”, the halacha refers to “Amen. Y’hei shmei rabah etc.” until “yitbarach”; By “kedusha”- the halacha refers to the community response of “kadosh, kadosh, kadosh” and “baruch kevod etc.”; By “barchu” the halacha refers also to the communal response (Shulchan Aruch Orach Chayyim 104,7; Mishna Berura 104, 26-29; Ishei Yisrael 32, 16). Regarding “Elokai N’tzor”- if you have already said “yihyu l’ratzon imrei etc.” (some say this before “elokai n’tzor”) you should participate out loud with the community. If you have not yet said this, it is recommended that you do so- otherwise the question of whether you are permitted or required to answer out loud is in dispute between the Shulchan Aruch and the R’ma (Orach Chayyim 122, 1) the Vilna Gaon and others (Ishei Yisrael 32 n. 59*).