Is Zakah (obligatory charity) due on the money saved for marriage?
Zakah is due on the money saved for marriage if it reached the Nissab (minimum amount liable for Zakah), and a whole lunar year had lapsed over possessing it.
What is the ruling o associations (Whereas a person who have money buys a commodity for a person and and gets a profit on it)?
It is permissible for a person to buy a commodity for someone's else and have a profit/loss on it
Is it permissible to swear by (Allah "The Living")?
Yes, it is permissible because "The Living" is one of Allah`s Attributes.
Is It Permissible to Divorce One's Wife for not Praying
All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon Prophet Mohammad and upon all his family and companions.
You should do your best to save her from hellfire by making her observe daily prayers on their prescribed times, even if this means giving her a generous incentive. However, if she insisted on her position, then it is permissible for you to divorce her. And Allah The Almighty Knows Best.