Luka reže kruh na dasci i kaže da je nož tup.

Yes. Croatian doesn’t have a separate “continuous” tense like English. The present tense often covers both:

• Luka reže kruh. = “Luka cuts bread / Luka is cutting bread.” Context decides whether it’s habitual or happening right now.

reže is the 3rd person singular present of rezati (“to cut”).
So reže = “(he/she/it) cuts / is cutting.”

rezati is imperfective, focusing on the process (“cutting”). That fits a scene description well.
A common perfective partner is odrezati (“to cut off / cut (something) up as a completed action”). For example:

• Luka je odrezao kruh. = completed result (“He cut the bread.”)

Croatian has no articles. Definiteness is inferred from context.

• reže kruh could be “cuts the bread” (a specific loaf) or “cuts bread” (bread in general).
  Speakers clarify with words like taj/ovaj (“that/this”) if needed:
• reže taj kruh = “cuts that bread.”

kruh is the direct object of reže, so it’s in the accusative.
For many masculine inanimate nouns, the accusative is identical to the nominative, so you don’t see a change:

• nominative: kruh
• accusative: kruh

After na meaning “on (a surface)” (location), Croatian uses the locative:

• na + locative = “on/at (location)” So daska (“board”) becomes locative singular dasci:
• daska (nom.)
• dasci (loc.)

Because there’s no movement.

• na + locative = location (where?): na dasci (“on the board”)
• na + accusative = movement toward (where to?): na dasku (“onto the board”)

So:

• reže kruh na dasci = he’s cutting while it’s on the board
• stavlja kruh na dasku = he puts the bread onto the board

i normally means “and,” coordinating two actions:

• reže ... i kaže ... = “(he) is cutting ... and (he) says ...” It can also have an “also/even” flavor in some contexts, but here it’s the straightforward “and.”

da introduces a content clause after verbs like “say/think/know”:

• kaže da je ... = “says that (it) is ...” It’s the standard way to report what someone says without quoting them directly.

Generally, with kaže in the sense “says (that) …,” da is the normal choice.
što is more typical in other structures (e.g., relative clauses, certain fixed expressions), but for reported speech kaže da ... is the default and safest.

je is the present tense of biti (“to be”) in 3rd person singular: “is.”
In the present tense, je is often used, and here it’s completely natural:

• kaže da je nož tup = “says that the knife is dull” In some styles and contexts, je can be omitted (nož tup) especially in headlines or very colloquial speech, but learners should treat je as the normal form.

Both are possible. Word order is flexible and depends on emphasis and rhythm.

• da je nož tup is very common after da, with the clitic je appearing early.
• da je tup nož is also possible, but it can sound like you’re emphasizing “a dull knife” as a phrase.
  Neutral and clear options include:
• da je nož tup
• da je nož tup (most typical)

nož is the subject of the subordinate clause da je nož tup.
Subjects are in the nominative, and nož is nominative singular.

Adjectives agree with the noun in gender, number, and case.
nož is masculine singular nominative, so the adjective is:

• masculine nominative singular: tup Compare:
• oštra nož is wrong (gender mismatch)
• tup nož (masc.) / tupa daska (fem.) / tupo staklo (neut.)

The ž is like the “s” in English measure / vision (IPA /ʒ/).
So:

• reže ≈ “reh-zhe”
• kaže ≈ “kah-zhe”
  (Approximate—Croatian has fairly consistent spelling-to-sound.)

Luka is a masculine name in Croatian, even though it ends in -a (which often signals feminine nouns). It declines like a masculine personal name:

• nominative: Luka
• genitive: Luke
• dative/locative: Luki
• accusative: Luku
  But in this sentence it’s just the subject, so it stays Luka.