this means the way to happiness. Not common. You'll see this more in the plural, as in "The Whys of Planning," which just means the reasons to plan. The Whys and Hows of Planning -- the reasons to plan and the ways to do it. the Hows are the ways to do something (how is a noun in this case) the whys and (the) wherefores is a set expression to mean the reasons for something

I've never heard of the "how of happiness"?!