دوست تو کجاست؟

A common transliteration is dust-e to kojâst?
Approx. pronunciation: doost-e to kojâst?

• دوست = doost (long oo)
• The linking sound -e (ezâfe) is usually pronounced even if not written.
• کجاست؟ = kojâst? (stress often toward the end: ko-JÂST)

Nothing is missing in meaning; it’s a writing convention. In Persian, possession is commonly expressed with ezâfe (-e) between the noun and the possessor:

• Spoken: دوستِ تو (dust-e to)
• Often written without the ezâfe marker: دوست تو
  In fully vowelled/teaching texts, you may see دوستِ تو to make the ezâfe explicit.

کجاست is basically کجا + است:

• کجا = where
• است = is (3rd person singular, formal/neutral “to be”)
  In writing, کجا است؟ is also possible, but کجاست؟ is extremely common and natural.

Yes, it’s normal. Persian commonly places the question word (کجا) close to the verb:

• دوستِ تو کجاست؟ ≈ Your friend is where?
  This is a standard, natural structure for “Where is X?” questions.

Yes, and it’s very common in everyday speech. دوستت means دوستِ تو with the pronoun attached:

• دوستِ تو کجاست؟ (a bit more explicit)
• دوستت کجاست؟ (more conversational/compact)
  Both mean the same thing; دوستت sounds more natural in casual spoken Persian.

تو is informal singular you (used with friends, family, peers, children).
For polite/formal or plural “you,” use شما:

• دوستِ شما کجاست؟ = Where is your friend? (polite/formal or plural “your”)

کجاست؟ is neutral and perfectly fine in speech. A more casual style often involves dropping است elsewhere, but کجاست؟ itself is already the common spoken form. In very colloquial speech you might hear other rephrasings like:

• دوستت کجاست؟ (most common casual version)
• دوستت کجاست الان؟ = Where’s your friend right now?

A natural pattern is rising intonation toward the end, with emphasis on کجاست:

• doost-e to koJÂST?
  Also, تو is usually not heavily stressed unless you’re contrasting (e.g., “your friend, not mine”).