I want to know how much happiness my Riolu currently has and I rather not resort to using calculations with return.
The friendship rater is in Konikoni City. These are the things she says when the Pokemon's happiness is a certain number.
255: "My! It feels incredibly close to you! Nothing makes it happier than being with you!"
200-254: "You clearly love your <Pokémon>, and you must spend a lot of time together."
150-199: "Hm. I'd say that you and <Pokémon> have the potential to be an even greater combo."
100-149: "Hmmm. I think…it feels friendly toward you. At least a little…"
50-99: "Hmmm… I'd say that you and your Pokémon still have a long way to go."
1-49: "What is going on here? Do you let it get knocked out a lot in battles or something? This is bad."
0: "Oh dear. You must be a merciless Trainer… Do you use Frustration or just not know better?"
For S/M, there should be a "Friendship Judge" in Konikoni City who will say one of several phrases depending on the happiness level of your Pokémon.
More information here.
You need to go to Konikoni City on Akala Island. Look for a female Veteran Trainer.