Does one have to say Amen, Borchu, Kedushah while they are learning and there is a Minyan going on which one is not Davening with?
If one has already answered Kedushah but hears a Minyan saying Kedushah, he should stop and say it with them.
See here for more details.
This answer is sponsored:
לע”נ רב יונה בן רב מאיר ע”ה