El greñado necesita la cuchilla de panadero.

Greñado here is being used as a noun, not as a verb. It refers to the scoring/cut made in the dough (or the process/result of that scoring, depending on context).

• greñar = the verb, to score bread dough
• greñado = the scoring, slash pattern, or cut

So in this sentence, el greñado is the subject: it is the thing that needs the blade.

Because greñado is treated as a masculine singular noun here.

In Spanish, nouns normally need an article when you are talking about a specific thing or a concept as a noun:

• el greñado = the scoring
• la cuchilla = the blade

Even if the English translation might sound more natural without the in some contexts, Spanish often uses the definite article more readily.

Because the subject is el greñado, which is singular.

• El greñado necesita... = The scoring needs...

If the subject were plural, the verb would also be plural:

• Los greñados necesitan... = The scorings / score marks need...

So necesita matches el greñado.

Cuchilla and cuchillo are related words, but they are not exactly the same.

• cuchillo = knife
• cuchilla = blade

In bread-making, cuchilla is more appropriate if the tool is specifically a blade used for scoring dough. So this sentence is talking about the blade itself, not just any knife.

Also, cuchilla is a feminine noun, so it takes la.

It means something like for a baker or used by a baker, and in natural English it may be translated as baker’s blade.

This structure is very common in Spanish:

• cuchilla de panadero = baker’s blade / baker’s scoring blade
• horno de panadero = baker’s oven
• sombrero de chef = chef’s hat

So de + profession/noun often describes the type, purpose, or association of something.

Because de panadero usually describes the kind of blade, not the blade belonging to one specific baker.

Compare:

• la cuchilla de panadero = a baker’s blade / a blade used by bakers
• la cuchilla del panadero = the baker’s blade = the blade belonging to a specific baker

So:

• de panadero = type or function
• del panadero = possession by a specific baker

Because la cuchilla de panadero is a direct object referring to a thing, not a person.

Spanish uses the personal a mainly with specific human direct objects:

• Veo al panadero. = I see the baker.
• Necesita la cuchilla. = It needs the blade.

Since la cuchilla is an object/thing, no a is used.

In standard Peninsular Spanish, c before e or i is usually pronounced like th in thin.

So necesita is approximately:

neh-theh-SEE-tah

More carefully: [neθeˈsita]

This is one of the big pronunciation differences between Spain and most of Latin America, where it would usually sound more like neh-seh-SEE-tah.

Ñ is pronounced like the ny sound in canyon.

So greñado sounds approximately like:

greh-NYAH-doh

That ñ is a separate letter in Spanish, not just an n with a mark on it. It changes the sound completely:

• ano and año do not sound the same
• greñado has that clear ny sound

Yes, but El greñado necesita la cuchilla de panadero is the most neutral and standard order:

Subject + verb + object

You could change the order for emphasis, but it would sound more marked:

• La cuchilla de panadero la necesita el greñado.

That puts emphasis on the baker’s blade. In normal usage, though, the original order is the most straightforward.

Grammatically, panadero is still a noun meaning baker, but in the phrase de panadero it behaves like a descriptive noun phrase, modifying cuchilla.

English often uses nouns directly before other nouns:

• baker’s blade
• bread knife
• chef hat

Spanish usually prefers:

• cuchilla de panadero
• cuchillo de pan
• gorro de chef

So panadero stays a noun, but the whole de panadero phrase describes the kind of blade.