Question: I daven nusach ashkenaz though occasionally daven in a sefardi shul on Shabbos morning. Is there any issue with me hearing parshas zachor there?
Answer: The Shulchan Aruch (OC 684:7) writes that there is a mitzva deoraisa to listen to parshas zachor.
R’ Zvi Pesach Frank (Har Zvi OC:4), R’ Yitzchak Yaakov Weiss (Minchas Yitzchak 3:9; 4:47:3) and R’ Moshe Sternbuch (Teshuvos Vehanhagos 1:154) write that as there are advantages to the ashkenazi pronunciation, one who usually davens with an ashkenazi pronunciation mustn’t change to a sefardi one.
Similarly, R’ Ovadia Yosef (Yabia Omer 6:C:11) explains that as there advantages to the sefardi pronunciation, one who davens with an sefardi pronunciation mustn’t change to an ashkenazi one. He writes that he’d regularly tell sefardi bachurim studying in an ashkenazi yeshiva to go to a sefardi shul to hear parshas zachor.
R’ Moshe Feinstein (Igros Moshe OC 3:5; 4:65) explains that during the time of the first beis hamikdash, everyone spoke with a similar pronunciation. It wasn’t until we were exiled, that slight changes crept in. While people shouldn’t change from one to the other, all pronunciations are equally valid.
R’ Zvi Pesach Frank (Mikraei Kodesh, Arba Parshiyos 7:n6) writes that one who usually davens with an ashkenazi pronunciation should be particular to listen to parshaz zachor read in as ashkenazi pronunciation (See Rivevos Ephraim 5:584:4; Piskei Teshuvos 685:10).
Nonetheless, R’ Ovadia Yosef (Yalkut Yosef 685:12) and R’ Shlomo Zalman Auerbach (Halichos Shlomo Purim 18:1) write that bedieved, one fulfils their obligation wherever they go.In conclusion, one should make the effort to listen to parshas zachor in one’s own nusach. If faced with no choice, one fulfils their obligation whichever shul they attend.