What is correct?(1) or (2)

1/ What goes this word refer to?

2/What goes this word refer?

If both, what is the difference btw them?

You need "does," not "goes."
And you need the "to."

What does this word refer to?
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How many countries will be participating? (1)


What does this word refer to? (2)

For (1) , Hancus wrote:

Only (1) seems correct to me, as "to participate in" doesn't exist as a phrasal verb.
Thus "in" is separate from the verb, and only used when the context continues with something.

Why didn't what Hancu said apply for (2)?

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He's asking I guess about

How many countries will participate in?

which I said it's incorrect.
But you don't want to give the answer?

"Refer to" requires the "to." It's a phrasal verb.

"Participate" does not require the "in." You do use it in some circumstances, but it's not always incomplete without it.