Wow, hardware disease is not a string I'd've expected!

Hey, my phone gave up on correcting I'd've :-)

@user62015 What makes you happy? is the question you should normally use.

You can say What does make you happy? in certain special situations, but it's less common.

You can use it to contrast with a negative: "I bet snails make you happy! After all, your name is Snailboat." "Not really. Snails don't make me happy." "Well then, what does make you happy?"

This is most common in informal spoken English. The auxiliary does is stressed. In formal writing, you wouldn't use does here.

(Note: the dialogue above is fictional. Snails actually do make me happy. I've just added do here to contrast with a negative.)

So as you can see, the version with do is fairly limited. As a learner, you should remember the version without do as the basic version of the sentence.

You can only add do under special circumstances, and even then, adding do isn't actually required.

So when do you have to add do, then?

(1) When you're forming a regular question, you need to swap the subject and auxiliary. If no auxiliary is present, you add the meaningless auxiliary do. It allows you to form a question without changing the meaning of the sentence.

(2) If you're asking a wh-question and the wh-word is the subject (or is part of the subject), you don't need to swap the subject and auxiliary, so you don't need to add do.

In your example, "What makes you happy?", the wh-word is the subject.

That means we don't need to add do, and we don't need to move the wh-phrase to the beginning of the sentence because it's already there.

(1A) Music makes you happy. (1B) What makes you happy?

Let's look at another example.

(2A) I ate pizza for dinner.

We want to make this into a question, and we're going to start by replacing the object pizza with the wh-word what.

(2B) I ate what for dinner?

Next, we move the wh-phrase to the beginning of the sentence:

(2C) what I ate __ for dinner

Now we want to invert the subject and auxiliary. But oh no! We don't have an auxiliary. We'll have to add do first:

(2D) what I did eat __ for dinner

Now we have an auxiliary, so let's swap it with the subject to finish making our question:

(2E) What did I eat __ for dinner?

In this question, do was required because we wanted to invert the subject and auxiliary, but we didn't have an auxiliary. Why did we want to invert them? Because it was a regular question and the wh-phrase was the object, not the subject.

That makes it different from example (1B).

In (1B), adding do only occurs under special circumstances.

But in (2E), it's required!

Does that help?