Кто‑нибудь знает, где находится аптека?

Кто‑нибудь means anyone / somebody.

• Кто by itself means who
• Кто‑нибудь means anyone, in a general, unspecified sense

So:

• Кто знает...? = Who knows...? / Does anyone know...? depending on context
• Кто‑нибудь знает...? more clearly means Does anyone know...?

In questions, -нибудь is very common when you mean any person at all.

Because кто‑нибудь is grammatically treated as singular in Russian.

Even though in English anyone refers to any person and can feel conceptually plural, Russian uses singular verb agreement with it:

• Кто‑нибудь знает...? = Does anyone know...?

So знает is the 3rd person singular form of знать (to know).

The comma separates two clauses:

• Кто‑нибудь знает = main clause
• где находится аптека = subordinate clause

Russian uses commas very regularly before subordinate clauses introduced by words like:

• где = where
• что = that/what
• когда = when
• почему = why
• если = if

So the comma here is required.

Both are possible, but they are slightly different in style.

• Где аптека? = Where is the pharmacy?
  Very natural in everyday speech; short and direct.

• Где находится аптека? = literally Where is the pharmacy located?
  A bit more formal or explicit.

In this sentence, находится adds the idea of being located. It is extremely common in Russian when asking where something is.

Находится is the 3rd person singular form of находиться.

In this sentence, находиться means:

• to be located
• to be situated

So:

• аптека находится = the pharmacy is located

It is not usually translated word-for-word as finds itself or anything like that, even though the verb historically relates to finding.

Because аптека is the subject of the clause где находится аптека.

In other words, the pharmacy is the thing that is located somewhere. Since it is the subject, it stays in the nominative:

• аптека = nominative singular

If another structure were used, the case might change, but in this sentence nominative is correct.

Yes, both are natural, but they have different tones.

• Где аптека?
  Very short, direct, and common.

• Кто‑нибудь знает, где находится аптека?
  Does anyone know where the pharmacy is?
  Sounds like you are asking a group.

• Вы не знаете, где находится аптека?
  Literally You don’t happen to know where the pharmacy is?
  A very common polite way to ask a stranger.

So the sentence you were given is especially suitable when speaking to several people at once.

Yes. Russian word order is flexible, though some versions sound more natural in certain contexts.

Standard version:

• Кто‑нибудь знает, где находится аптека?

You might also hear:

• Кто‑нибудь знает, где аптека?
• Где находится аптека, кто‑нибудь знает? — possible, but more marked or conversational

The original order is the most neutral and natural for a learner to use.

It is pronounced approximately like:

• kto NEE-boot'

The stress is on ни́ in нибудь.

It is written with a hyphen because Russian indefinite pronouns and adverbs with particles like -нибудь, -то, and -либо are normally hyphenated:

• кто‑нибудь = anyone
• что‑то = something
• где‑либо = anywhere

So the hyphen is part of the standard spelling.

These are easy to confuse:

• кто‑нибудь = anyone / someone or other
  Often used in questions, conditions, or when the specific person does not matter

• кто‑то = someone
  Usually refers to an actual but unidentified person

• никто = no one

Examples:

• Кто‑нибудь знает? = Does anyone know?
• Кто‑то знает. = Someone knows.
• Никто не знает. = No one knows.

So in your sentence, кто‑нибудь is the right choice because the speaker is asking whether anyone at all knows.

It is fairly neutral.

• Not especially formal
• Not slangy
• Natural in everyday speech

The part где находится аптека is a little more formal or careful than simply где аптека, but the whole sentence still sounds normal and natural.

If you were asking passersby politely, many speakers might prefer:

• Извините, вы не знаете, где находится аптека?

But the original sentence is completely correct and useful.