You would use the word happieness in a sentince like;

"Your happieness is My happieness"

"Your smile brings me happieness"

I guess you may refer to the context that allows you to use those expressions, so it's just a way to express your positive emotions or gratitude regarding another person, or a certain experience you have, etc.  like: I'm happy for you/ I feel fortunate to have a supportive family.