La camarera me guiñó un ojo cuando reconoció a mi hermana.

Here, me shows who received the wink. In Spanish, guiñar un ojo often takes an indirect object:

La camarera me guiñó un ojo = the waitress winked at me / to me.

English uses at, but Spanish normally uses an indirect object pronoun:

• me = to me
• te = to you
• le = to him/her

So me does not mean myself here; it means to me.

Because guiñar un ojo is a fixed, very common expression. It literally refers to closing one eye briefly, so Spanish uses un ojo.

You do not normally say sus ojos here, because the owner of the eye is already obvious: it is the waitress's eye. Spanish often avoids possessives when the meaning is clear.

Because a wink involves one eye, not both. If both eyes close briefly, that is not normally described as guiñar un ojo.

So:

• guiñar un ojo = to wink
• literally, to close one eye briefly

Both verbs describe completed actions in the past:

• guiñó = she winked
• reconoció = she recognized

The preterite is used because these are seen as single, finished events in a past sequence. The sentence is basically telling a short event: first she recognized the sister, then she winked.

If the imperfect were used instead, it would sound more like background, repetition, or an ongoing situation.

They are standard third-person singular preterite forms:

• guiñar → guiñó
• reconocer → reconoció

In these forms, Spanish writes an accent on:

• -ó for many -ar verbs
• -ió for many -er/-ir verbs

The accent shows the correct stress and is part of the normal spelling.

That is the personal a. Spanish usually uses a before a specific human direct object.

So:

• reconoció a mi hermana
• vio a Juan
• escuché a tu madre

Here, mi hermana is a specific person, so a is required.

Here it means recognized.

This is an important difference:

• conocer = to know, to be acquainted with, or to meet for the first time
• reconocer = to recognize, identify, realize who someone is

So reconoció a mi hermana means the waitress realized who the sister was, probably because she had seen or known her before.

The most natural subject is still la camarera.

So the sentence means: the waitress winked at me when she recognized my sister.

Spanish often leaves subject pronouns unstated, because the verb form and context make the subject clear. Since la camarera is already the subject of the main clause, readers normally understand that she is also the subject of reconoció.

Because Spanish often omits subject pronouns when they are not needed.

Instead of saying: ...cuando ella reconoció a mi hermana

Spanish normally just says: ...cuando reconoció a mi hermana

The ending -ó already tells you it is he/she in the preterite, and the context tells you it is la camarera. Adding ella would usually be for emphasis, contrast, or clarification.

In modern standard Spanish, possessive adjectives like mi, tu, su, nuestro normally replace the article.

So you say:

• mi hermana
• tu padre
• su casa

not:

• la mi hermana

That older structure exists only in very special or archaic uses, not in normal modern Spanish.

Yes. That is completely natural and means the same thing.

Spanish is flexible with word order, especially with time clauses like cuando...:

• La camarera me guiñó un ojo cuando reconoció a mi hermana.
• Cuando reconoció a mi hermana, la camarera me guiñó un ojo.

The second version puts a little more focus on the moment of recognition.

Roughly gee-NYO.

A few details:

• gui here sounds like gi; the u is silent
• ñ sounds like the ny in canyon
• the stress is on the last syllable: gui-ÑÓ

So: gee-NYO is a useful approximation for an English speaker.