Mi ne volas plendi pri la laboro hodiaŭ.

In Esperanto, ne normally goes directly before the word or idea it negates.

So:

Mi ne volas plendi pri la laboro hodiaŭ
means that the wanting is negated: I do not want to complain...

Compare that with:

Mi volas ne plendi pri la laboro hodiaŭ
This would mean something more like I want not to complain... or I want to avoid complaining...

Both are possible, but they are not quite the same. The original sentence is the most natural way to say it.

The ending -i is the infinitive ending in Esperanto. It is the basic dictionary form of the verb, like to complain in English.

So:

• volas = want
• plendi = to complain

After voli, Esperanto normally uses an infinitive:

• Mi volas manĝi = I want to eat
• Mi volas iri = I want to go
• Mi volas plendi = I want to complain

Pri is the usual preposition for about, concerning, or regarding.

The verb plendi is commonly used with pri when you say what someone is complaining about:

• plendi pri la vetero = complain about the weather
• plendi pri la laboro = complain about the work

So this is a standard and natural combination: plendi pri.

La is the Esperanto definite article, meaning the.

Using la laboro suggests a specific work situation, job, or piece of work that is already understood from context.

• pri la laboro = about the work / the job
• pri laboro = about work in general

So the sentence with la sounds more specific.

The -n ending marks the direct object in Esperanto.

But la laboro here is not a direct object of the verb. It is the object of the preposition pri.

After a preposition, nouns usually do not take -n:

• pri la laboro
• kun mia amiko
• en la domo

So laboro stays laboro, not laboron.

It can mean either one, depending on context.

Laboro is a broad word meaning work, labor, or sometimes job/work situation.

So in this sentence it could mean:

• the work you are doing
• your job
• the workload
• the work situation

If someone wanted to be more specific, they might choose a different word, but laboro is very normal here.

Hodiaŭ is an adverb meaning today.

It does not change form. It does not need an ending like -e to be an adverb, because some Esperanto adverbs are built-in words.

So:

• hodiaŭ = today
• nun = now
• jam = already

In the sentence, hodiaŭ tells us when the speaker does not want to complain.

No. Esperanto word order is fairly flexible.

The end position is very natural:

Mi ne volas plendi pri la laboro hodiaŭ.

But you could also say:

• Hodiaŭ mi ne volas plendi pri la laboro.
• Mi hodiaŭ ne volas plendi pri la laboro.

These all work. The version with hodiaŭ at the end is smooth and neutral.

Usually, yes, you should include mi.

Esperanto verbs do not change according to person:

• mi volas
• vi volas
• li volas
• ili volas

Because volas looks the same for all persons, the subject pronoun is normally needed.

So Mi ne volas... is the standard form.

Esperanto stress is almost always on the second-to-last syllable.

Hodiaŭ is pronounced roughly ho-DI-aŭ.

A few helpful points:

• h is pronounced
• di sounds like dee
• aŭ is a diphthong, somewhat like ow in English

So the stress falls on di.

Because of hodiaŭ, the sentence most naturally means that the speaker does not want to complain today.

It does not necessarily mean the speaker never complains. It only limits the statement to today.

So the idea is something like:

Today, I don’t want to complain about the work.

That time word gives the sentence its specific scope.