Kannst du mir sagen, ob in der Suppe Paprika oder Zucchini sind?

Because the main clause is a yes/no question.

In German yes/no questions, the finite verb usually comes first:

• Du kannst mir sagen ... = You can tell me ...
• Kannst du mir sagen ...? = Can you tell me ...?

Here, kannst is the finite form of können, and du is the subject.

Mir means to me.

It is the dative form of ich:

• ich = I
• mich = me
• mir = to me / for me

The verb pattern is:

• jemandem etwas sagen = to tell someone something

So:

• Kannst du mir sagen ... = Can you tell me ...

Ob is used for an indirect yes/no question. It means whether or sometimes if.

So:

• Kannst du mir sagen, ob ... = Can you tell me whether ...

Why not the others?

• dass introduces a statement clause: that
• wenn usually means when or if in conditional/time meanings

Compare:

• Ich weiß, dass Gemüse in der Suppe ist. = I know that there are vegetables in the soup.
• Ich weiß nicht, ob Paprika in der Suppe ist. = I don’t know whether there is bell pepper in the soup.
• Wenn Paprika in der Suppe ist, esse ich sie nicht. = If there is bell pepper in the soup, I won’t eat it.

Because the clause after ob is a subordinate clause, and in German subordinate clauses the conjugated verb goes to the end.

So the structure is:

• Main clause: Kannst du mir sagen ...
• Subordinate clause: ob in der Suppe Paprika oder Zucchini sind

That is a very common German pattern:

• Ich weiß, dass er kommt.
• Sie fragt, ob du Zeit hast.
• Kannst du mir sagen, ob ... sind?

Because this is about location, not movement.

The preposition in can take:

• dative for location: in der Suppe = in the soup
• accusative for movement into something: in die Suppe = into the soup

Here the vegetables are already in the soup, so German uses the dative:

• in der Suppe

In German, ingredient names are often used without articles when you are talking generally about what a dish contains.

So this sounds natural:

• In der Suppe sind Paprika oder Zucchini.

This is similar to ingredient-list style language: you are naming the ingredients, not focusing on a specific individual vegetable.

If you add articles, the meaning changes a bit:

• eine Zucchini = one zucchini
• eine Paprika = one bell pepper

Without articles, the sentence sounds more like does the soup contain paprika/bell pepper or zucchini?

The sentence treats Paprika and Zucchini as ingredients or pieces of vegetables in the soup, so plural sind sounds natural.

In food contexts, German often thinks in terms of pieces/chunks/ingredients rather than one whole vegetable.

Also note:

• Zucchini has the same form in singular and plural
• Paprika can also be understood as an ingredient name rather than a clearly marked singular count noun in this kind of sentence

So sind works well here.

You may also hear ist in some contexts if the speaker is thinking of the ingredient more like an uncountable substance:

• ... ob Paprika oder Zucchini drin ist

That is also something you may hear in everyday speech.

Here it almost certainly means bell pepper.

In German, Paprika often means the vegetable bell pepper, not just the powdered spice.

If someone wants to be very clear about the spice, they might say:

• Paprikapulver = paprika powder

In this sentence, because it is paired with Zucchini, the natural reading is bell pepper as a vegetable ingredient.

No, German word order is somewhat flexible inside the clause, as long as the verb stays at the end.

So these are both natural:

• ..., ob in der Suppe Paprika oder Zucchini sind
• ..., ob Paprika oder Zucchini in der Suppe sind

The difference is mainly focus or emphasis.

• ob in der Suppe ... puts the location earlier
• ob Paprika oder Zucchini ... puts the ingredients earlier

Both are fine.

In normal conversation, oder presents the two alternatives the speaker wants clarified.

So the sentence basically means:

• Is it bell pepper or zucchini in the soup?

It often suggests one of the two, but everyday language is not always logically strict. If you want to be completely explicit that both are possible, you could say:

• ..., ob in der Suppe Paprika, Zucchini oder beides sind
• ..., ob Paprika oder Zucchini oder beides drin ist

So oder usually sets up the alternatives, but context decides how strict the contrast is.

Yes. A very everyday version would be:

• Kannst du mir sagen, ob Paprika oder Zucchini in der Suppe sind?

A more conversational version could be:

• Weißt du, ob da Paprika oder Zucchini drin sind?

Here:

• da = there / in it, depending on context
• drin = inside, in there

That version sounds especially natural in casual spoken German.

You would use Sie instead of du:

• Können Sie mir sagen, ob in der Suppe Paprika oder Zucchini sind?

Changes:

• Kannst du → Können Sie

Everything else can stay the same.

This is the standard polite form for speaking to a stranger, customer, server, or someone in a formal situation.