هل أنت هنا اليوم؟

هل is a question particle used mainly for yes/no questions in Modern Standard Arabic. It does not have a direct English equivalent; it simply marks the sentence as a question.
You can often drop it in speech or informal writing and rely on intonation: أنت هنا اليوم؟ still works as a yes/no question.

In Arabic, present-tense sentences often omit the verb to be. This is a normal nominal sentence pattern:

• أنت (subject) + هنا (predicate/adverb of place) + اليوم (time)
  If you needed past or future, Arabic typically uses a verb like كان (was) or سيكون (will be).

It depends on what you want to emphasize:

• هل أنت هنا اليوم؟ is explicit and clear: Are you here today?
• You could omit أنت only if the subject is already known from context, but in MSA it’s common to keep it for clarity.
  In many real situations, speakers shorten it to هل أنت هنا؟ or أنت هنا اليوم؟ rather than dropping أنت completely.

As written (without vowel marks), أنت is ambiguous in everyday unvowelled Arabic text, but in fully vowelled MSA:

• Masculine singular: أَنْتَ
• Feminine singular: أَنْتِ
  So the sentence could be directed to either, unless context (or vowel marks) clarifies it.

A common fully-vowelled form is:
هَلْ أَنْتَ هُنَا الْيَوْمَ؟
Notes:

• هَلْ ends with sukūn because it’s a particle.
• أَنْتَ is masculine; for feminine it’s أَنْتِ.
• الْيَوْمَ often appears with fatḥa in careful MSA as a time adverb in context.

A practical pronunciation guide:

• هل = hal
• أنت = anta (masc.) / anti (fem.)
• هنا = hunā (the final ā is long)
• اليوم = al-yawm (often pronounced with a slight linking: al-yawm)

A rough IPA (masculine): hal ʔanta hunā aljawm?
The أ in أنت is a real glottal stop sound (ʔ), especially in careful pronunciation.

Yes. اليوم is an adverb of time and is fairly flexible. Common options:

• هل أنت هنا اليوم؟ (very natural)
• هل أنت اليوم هنا؟ (also natural; slightly more focus on today)
• هل اليوم أنت هنا؟ (possible, but more marked/emphatic)

Arabic word order often shifts to highlight what the speaker cares about.

Both can form a yes/no question in MSA:

• هل أنت هنا اليوم؟ is the most common, neutral yes/no pattern.
• أأنت هنا اليوم؟ uses the interrogative hamza أَ and can sound a bit more formal or emphatic, sometimes implying surprise or contrast depending on context.
  In unvowelled writing, أأنت is sometimes avoided because the double hamza looks heavy.

Yes, you can answer briefly:

• نعم. = Yes.
• لا. = No.

More natural full answers often repeat key information:

• نعم، أنا هنا اليوم.
• لا، لستُ هنا اليوم. (I am not here today.)
  In MSA, لستُ is a common way to negate I am not in the present.

You normally do not say في هنا in MSA for this meaning. هنا already means here as a complete adverb of place.
You use في with a noun location, for example: في البيت (in the house), في المكتب (in the office).

In Arabic typography, the standard question mark is ؟ (mirrored). So you’ll often see: هل أنت هنا اليوم؟
If you’re writing Arabic inside an English context, you may still encounter ?, but ؟ is the conventional Arabic punctuation.

It depends on the dialect, but many dialects drop هل and use intonation:

• Levantine: إنت هون اليوم؟
• Egyptian: إنت هنا النهارده؟
• Gulf: إنت هني اليوم؟ (varies)

MSA هل أنت هنا اليوم؟ is correct and widely understood, but it sounds more formal/bookish in casual conversation.