Je ne sais pas comment réagir maintenant.

Here is the breakdown:

• Je = I
• ne ... pas = the standard French negation, meaning not
• sais = know from the verb savoir
• comment = how
• réagir = to react
• maintenant = now

So the structure is:

• Je ne sais pas = I do not know
• comment réagir = how to react
• maintenant = now

A very literal version is:

• I do not know how to react now

In standard French, negation usually has two parts:

• ne before the conjugated verb
• pas after the conjugated verb

So:

• Je sais = I know
• Je ne sais pas = I do not know

This is the normal written form and the form usually taught to learners.

Yes. In everyday spoken French, many speakers drop ne:

• Je ne sais pas comment réagir maintenant = standard written and careful spoken French
• Je sais pas comment réagir maintenant = very common in casual speech

As a learner, it is best to understand both, but use the full form ne ... pas in writing and in formal situations.

French has two common verbs that can both relate to knowing, but they are used differently:

• savoir = to know a fact, know how, know information
• connaître = to know a person, place, or be familiar with something

Here, the meaning is I do not know how to react, so French uses savoir.

Correct:

• Je ne sais pas comment réagir

Not natural here:

• Je ne connais pas comment réagir

That sounds wrong because connaître is not used for knowing how in this way.

In English, we say how to react.

In French, the equivalent structure is simply:

• comment + infinitive

So:

• comment réagir = how to react

French does not need an extra word like to here. The infinitive réagir already carries that meaning.

Other examples:

• Je sais comment faire = I know how to do it
• Elle explique comment utiliser l’appareil = She explains how to use the device

Because it depends on savoir in the expression savoir comment + infinitive.

The sentence is not saying:

• I do not know how I react

It is saying:

• I do not know how to react

So French uses the infinitive réagir, just like English uses to react.

Because ne ... pas surrounds the conjugated verb, not the infinitive.

In this sentence, the conjugated verb is:

• sais

So the negation goes around it:

• Je ne sais pas

The verb réagir is an infinitive, so it is not the verb being directly negated.

This is a very important French pattern:

• Je ne veux pas partir = I do not want to leave
• Il ne peut pas venir = He cannot come

The negation surrounds veux or peut, not partir or venir.

Yes, comment is an interrogative word meaning how, but here it appears inside an indirect question.

Direct question:

• Comment réagir ? = How should one react? / How to react?

Indirect question:

• Je ne sais pas comment réagir = I do not know how to react

So even though the whole sentence is not a question, comment still introduces the idea of how.

Sais is the present tense of savoir, first person singular:

• je sais = I know

So:

• Je ne sais pas = I do not know

French often uses the present tense here exactly the way English does.

Maintenant means now, and placing it at the end is very natural:

• Je ne sais pas comment réagir maintenant

This sounds like:

• I don’t know how to react now

You can sometimes move it for emphasis, for example:

• Maintenant, je ne sais pas comment réagir
• Je ne sais pas maintenant comment réagir

But the original sentence is the most neutral and natural choice in many situations.

Usually it is closest to react, but depending on context it can sometimes feel like respond.

• réagir often suggests an emotional, immediate, or situational reaction
• répondre usually means to answer or to reply

So in this sentence, réagir is the right verb because the idea is about how to behave or respond emotionally/in the moment, not just how to answer someone verbally.

A careful pronunciation is roughly:

• Zhuh nuh say pah koh-mahn ray-ah-zheer man-tuh-nahn

A few useful notes:

• Je sounds like zhuh
• ne is often very light, and in casual speech may disappear
• sais sounds like say
• comment sounds like koh-mahn
• réagir has three clear parts: ré-a-gir
• maintenant has nasal vowels, so its ending does not sound like a clear English n

In casual speech, you may hear something closer to:

• J’sais pas comment réagir maintenant

Yes, but it means something a little different.

• Je ne sais pas comment réagir maintenant = I don’t know how to react now
• Je ne sais pas quoi faire maintenant = I don’t know what to do now

The first focuses on your reaction. The second focuses on your next action.

Sometimes both could work, but they are not exactly the same.