Ukiwa na swali, uliza darasani.

Ukiwa comes from:

• u- = you (singular)
• -ki- = if/when
• -wa = be

So ukiwa literally means if/when you are.

In this sentence, it combines with na to make ukiwa na..., which is the Swahili way of saying if/when you have....

Because Swahili often expresses to have as to be with.

So:

• kuwa na = to have / literally to be with
• ukiwa na swali = literally if/when you are with a question

That is why the wording may look different from English, even though the meaning is natural in Swahili.

Yes. In many contexts, -ki- can mean if, when, or whenever, depending on the situation.

So Ukiwa na swali, uliza darasani can feel like:

• If you have a question, ask in class
• When you have a question, ask in class
• even Whenever you have a question, ask in class

The exact nuance comes from context.

Kuuliza is the infinitive, meaning to ask.

When giving a direct command to one person, Swahili usually drops the ku- infinitive prefix:

• kuuliza = to ask
• uliza! = ask!

So uliza darasani is the singular imperative: ask in class.

It is a command to one person.

• uliza = ask! (to one person)
• ulizeni = ask! (to more than one person)

So this sentence is addressing a single learner. If you wanted to address a group, you could say:

• Mkiwa na swali, ulizeni darasani.

That would mean If you have a question, ask in class when speaking to several people.

Darasa means class or classroom.
The ending -ni is a locative ending, often meaning in, at, or to a place.

So:

• darasa = class / classroom
• darasani = in class / in the classroom

In this sentence, darasani means something like in class or during class.

Swali means question.

Its plural is maswali:

• swali = question
• maswali = questions

So if you wanted to say If you have questions, ask in class, you could say:

• Ukiwa na maswali, uliza darasani.

Or, if speaking to several people:

• Mkiwa na maswali, ulizeni darasani.

Because Swahili usually includes the subject inside the verb.

In ukiwa, the u- already means you.
And in uliza, the imperative form is naturally understood as a command to you.

So Swahili does not need a separate word like English you here.

Yes, that is also natural.

Compare:

• Ukiwa na swali, uliza darasani.
• Kama una swali, uliza darasani.

The second version uses:

• kama = if
• una = you have

Both are understandable and natural.
Ukiwa na swali may sound a bit more like when/if you have a question, while kama una swali is a very direct if you have a question.

This order is very natural:

• condition first: Ukiwa na swali
• then the command: uliza darasani

So the structure is:

• If/when X, do Y

That is a very common Swahili pattern. The sentence sounds clear and normal as written.