"Où que" is a reinforced question word, exactly equivalent to a simple "où" or to "où est-ce que" or "où c’est que".

Those reinforced forms aren’t unique to "où", but can be found with any question word that’s been fronted to the begining of a sentence:

Quand tu pars?

Quand est-ce que tu pars?

Quand c’est que tu pars?

Quand que tu pars?

That last version with "question word+que" is quite stigmatised and rarer in Europe, but enjoys more vitality in North America.

At the beginning of the 20th century, it was quite common in the western part of France but its usage has dwindled since.

Corpus studies in Quebec French (CFPQ, around 2000) and France French (Corpus d’Orléans, 1968-71) have shown that "pourquoi que" and "comment que" are the most common, followed by "où que" while "quoi que" and "qui qui" are almost completely absent, as are prepositional question words like "de quoi que".

Such a form is indeed colloquial, and equivalent in meaning to more formal variants such with inversion.

It’s substandard in French such as spoken in France; it can be used when talking to small children barely out of babyhood or still babies; it is also used on the tone of mild remonstrance when something is expected to be somewhere but is not found there; it is also used when the person talking does not really believe that something that’s been talked about really exists; finally, it is used in a somewhat jocular way and for no particular reason.