1. It’s not a matter of fitting a form to a context or a matter of register but a matter of personal preference, the modern trend being for the less educaded and also more and more for the educated to say “Il est où?”. As well and on a similar level of colloquial speech French people use “Où il est?”; the traditional, irreproachable form remains however “Où est-il?”.

Whether a form is odd or not is a matter of whom you are talking to; an open minded hearer would find no ground for criticizing the use of “Où est-il?” in any circumstance; it is a personal choice and a correct one. Similarly one should not be critized for using the other forms as, while they are not ideal forms, they are still widely used. However people in France as anywhere else are of all sorts and either one of the forms considered might occasionally be found unpleasant; I will not conclude by the (I think) American adage that says “You can’t please everyone you’ve got to please yourself.” but I’ll suggest that maybe someone should try to know whom he/she is talking to, first, and so prepare him/herself to handle the two main forms in spoken French instead of limiting him/herself to the use of just one.

2. Justin est OÙ?
   This is also possible in French, with a special emphasis on “où”, there being quite a few variants of the emphatic intonations you can use and it being up to you to duplicate what you might have heard. However Justin must be somewhere as in the chimney or in the refrigerator!

It’s a matter of formality. “Où est-il ?” is traditionally “correct”, I would use it in writing but not in a normal conversation (it sounds too formal). “Il est où ?” is the one I would normally use in a colloquial setting, but I wouldn’t use it in formal writing.

It is a matter of register.

The most formal is:

Où est-il ?

It will be used in written French and formal situations, but of course nobody will blame you for using it in other situations, especially as a foreigner.

Then comes what is certainly the form most used in spoken French, where the pronoun-verb inversion has been dropped:

Où il est ?

Finally, there is the colloquial form when the intonation is used to mark the interrogation :

Il est où ?

While the two first forms are usually pronounced with two syllables [wɛ.til] and [wi.lɛ], the third one requires three syllables [i.lɛ.u]. The first one is sometimes dropped in colloquial spoken French leading to l’est où ?

When you want to specify the person, you might use several forms:

Où est Justin ? formal / standard
Justin est où ? colloquial

But not the middle form:

Où Justin est ? (should be Où Justin est-il ?)

Often, the name is added to the pronoun form, e.g.:

Où il est, Justin ?
Il est où, Justin ?
Justin, il est où ?