Is there a typographic difference between a or i with ogonek versus a or i
with retroflex hook? If I'm looking at a sample, what are the
distinguishing characteristics that I can use to determine whether I'm
seeing an ogonek or a retroflex hook?
U+0322 RETROFLEX HOOK is an artifact of Unicode.
The official IPA chart shown at http://www2.arts.gla.ac.uk/IPA/fullchart.html indicates a retroflex series of consonants with symbols created by modifying the shape of corresponding charactes in the Dental/Alveolar/Postalveolar column to add a right-turning hook to the letter.
The resulting symbols indicate sounds made in the same way as the sounds associated respectively with the corresponding characters in the Dental/Alveolar/Postalveolar column, but with the tip of the tongue bent back so that its tip touches the roof of the mouth behind the alveolar ridge.
But no independant retroflex hook is indicated among the IPA diacritics.
However linguists do use non-standard notations, so a linguist might wish to modify some other symbol on occasion.
For example, a small capital D is sometimes used for the sound that IPA indicates by U+027E LATIN SMALL LETTER R WITH FISHHOOK. A linguist using that convention might wish the corresponding retroflex consonant to be indicated by a small capital D with a right turning hook beneath it.
What would really be wanted would be a modified small capital D with the retroflex hook attached to the lower left corner of the D and the serif at that point dropped.
U+0322 RETROFLEX HOOK could be used in such cases with a suitably intelligent font or as a workable compromise with an unintelligent font.
I suppose a RETROFLEX HOOK might be used with vowels, to indicate the vowel is being made with the tongue bent back (but without actual closure between the tip of the tongue and the roof of the mouth) but I have *never* seen such, probably because such tongue positioning does not produce noticeable modification in the pronunciation that would not be far more easily and understandably indicated by other conventions.
There is a linguistic tradtion of using ogonek or an ogonek-like hook beneath a vowel or consonant to indicate a more open pronounciation, often seen in treatments of pronunciation of Old English and Middle English.
This convention was formerly accepted by the IPA but has since been dropped by them. There is no modification of the shape of the base character. In phonetic use this linguistic ogonek was usually centered horizontally on the base character (even with _a_) which is not done with characters modified for show a retroflex hook.
Ogonek is also used to indicate nasalization of a vowel by some.
Jim Allan