1) Why do so many chashuve people learn during chazaras hashas, when it’s not permitted?
2) Am I allowed to learn during birchas krias shma (eg while waiting for chazan to say “emes”)?
- I can’t answer what I don’t know, maybe they don’t realize that it isn’t permitted. Look in Piskei Teshuvos 124-8, and that might help you.
- Learning with one’s mouth is not allowed during birkas kriyas shema, however if it is only with your eyes, the Rema (O:CH 68-1) says that it isn’t assur, however he isn’t very happy about it, because it could eventually lead to talking.