How much percentage of your take home salary do you give to your parent(s)?

As long as what you give makes your parents happy. If they are the demanding kind, then well you got to calibrate their expectations

Depends on your situation, best is to have a chat with your parents.

To each his/her own ?

Hi, you could take a look at this article on giving parents money. It also mentions non-monetary ways of giving back to your parents.