Trading after the Azaan of Jumuah

Q: I would like to know which Azaan is referred to in the Quranic ayat which prohibits us from conducting any business after the Azaan of Jumuah, is it the first Azaan or the second which is given infront of the mimbar? Secondly what are the consequences with regards to the wealth earned after
the Azaan has gone?

Girls going to universities

Q: I am a 23 years old girl studying in a medical university. I wanted to ask that can I continue my studies in the medical university? Is it allowed
in Islam to get education? The university is co-education but I don't talk to any male. I go to university in proper parda so can I continue it? I have heard that a female cannot go out of home without a mahram. As I don't have a brother, or a husband nor can my father go with me so in such a case is it permitted in Islam to go?

Animal euthanasia

Q: I'm working in animal an animal hospital and  sometimes we got patients like horses in very bad conditions in pain so we use a drug that can kill in seconds. Is there anywhere in quran or hadith or shariya that we shouldn't kill these kind of patients that are in pain?