Q. 1. What is the Catholic Church policy regarding attending non-Catholic services?
A. 1. The answer to your question varies depending on the circumstances.
Since Vatican II, in the spirit of ecumenism, the faithful are encouraged to visit non-Catholic services for educational purposes. At the same time, they cannot receive communion from non-Catholic Churches, nor participate in prayers or singing when such conflicts with Catholic teachings. In other words, you are welcome to visit non-Catholic Churches as an observer for the purpose of leaning about other faiths, but you cannot participate.
Visiting a non-Catholic Church cannot be substituted for one's Sunday obligation to attend Holy Mass in a Catholic Church. The penalty for failing to do so is the committing of a mortal sin. So if you visit a non-Catholic Church on a Sunday, you still have to go to a Catholic Church on that day.