Learn Hardcore Croatian: On pokušava ne kihnuti na sastanku. - He is trying not to sneeze at the meeting.

In a specific situation like a meeting, the idea is usually “He is trying not to (let himself) sneeze even once,” so the perfective kihnuti fits better:

On pokušava ne kihnuti na sastanku.
He is trying not to sneeze (even once) in the meeting.

If you said:

On pokušava ne kihati na sastanku.

it would sound more like “He is trying not to be sneezing at the meeting” (avoiding the general activity of sneezing there), which is possible but less natural for this context.

Why is the negation ne in ne kihnuti and not ne pokušava kihnuti?

The position of ne changes the meaning:

On ne pokušava kihnuti.
He is not trying to sneeze.
(He is doing something else; there is no attempt.)
On pokušava ne kihnuti.
He is trying not to sneeze.
(There is an attempt, but the thing he’s avoiding is the sneeze.)

In your sentence the important idea is that he is trying, but what he is trying to do is not sneeze, so ne goes with kihnuti, not with pokušava.

Could I also say On pokušava da ne kihne na sastanku? Is that correct, and is there a difference?

Yes, that is also correct Croatian:

On pokušava ne kihnuti na sastanku.
On pokušava da ne kihne na sastanku.

Both mean “He is trying not to sneeze at the meeting.”

Differences:

ne kihnuti – infinitive construction (more neutral, very common in standard Croatian).
da ne kihne – da
- finite verb (3rd person singular).
  This pattern is also common, and often feels a bit more colloquial or conversational in many contexts.

Semantically here they’re almost identical. As a learner, you can safely use the infinitive after pokušavati/pokušati:

pokušava ne + infinitive
pokušava + infinitive

Why is it na sastanku and not u sastanku?

In Croatian, you typically use na + locative for events, organized activities, and “sessions” of things:

na sastanku – at the meeting
na koncertu – at the concert
na predavanju – at the lecture
na nastavi – in class

u tends to be used more for physical interior space:

u sobi – in the room
u kući – in the house
u zgradi – in the building

A sastanak (meeting) is thought of as an event or session, not a container, so you say na sastanku.

What case is sastanku, and how is it formed from sastanak?

Sastanku is the locative singular form of the noun sastanak (meeting).

Pattern:

Nominative (base form): sastanak – a meeting
Genitive: sastanka
Dative: sastanku
Accusative: sastanak
Vocative: sastanče (rarely used)
Locative: sastanku
Instrumental: sastankom

With preposition na meaning “at (an event)” you use the locative:

na sastanku – at the meeting
na koncertu – at the concert

Is the subject On necessary? Could I just say Pokušava ne kihnuti na sastanku?

You can absolutely drop On:

Pokušava ne kihnuti na sastanku.

Croatian is a pro‑drop language: the verb ending usually shows the person and number, so subject pronouns are often omitted if the context is clear.

You use On mainly:

for emphasis (e.g. “He is trying, not someone else”), or
when you need to avoid ambiguity.

In ordinary context, leaving it out is perfectly natural.

Does pokušava mean “he tries” or “he is trying”? Does Croatian have a separate -ing form?

Pokušava can mean both:

He tries (habitual, general)
He is trying (right now, in progress)

Croatian does not have a special -ing form like English. The present tense does double duty:

On pokušava ne kihnuti na sastanku.
Depending on context, this can mean:
- In general, at meetings he tries not to sneeze, or
- Right now, in this particular meeting, he is trying not to sneeze.

Usually the context (or extra words like upravo sada = right now, uvijek = always) clarifies the intended meaning.

What is the difference between kihnuti and kihati?

They are two aspects of the same basic action “to sneeze”:

kihnuti – perfective
- one completed sneeze (or the idea of a single act)
- answers What happens (once)?
- e.g. Odjednom je kihnuo. – Suddenly he sneezed.
kihati – imperfective
- ongoing or repeated sneezing (the process)
- answers What is (was) happening?
- e.g. Cijeli dan kiše i kihati. – He’s been coughing and sneezing all day.

In pokušava ne kihnuti, the perfective matches the idea of preventing a single sneeze in that meeting.

Can I change the word order, for example On na sastanku pokušava ne kihnuti or On pokušava na sastanku ne kihnuti?

Yes, Croatian word order is more flexible than English, but changes in order can change emphasis.

All of these are grammatically possible:

On pokušava ne kihnuti na sastanku.
Neutral; focus is on “trying not to sneeze at the meeting.”
On na sastanku pokušava ne kihnuti.
Slight emphasis on na sastanku (“It’s at the meeting that he’s trying not to sneeze”).
On pokušava na sastanku ne kihnuti.
A bit marked; you’re inserting na sastanku into the middle of the verb phrase. Still understandable, but (1) is more natural.

As a learner, prefer version (1); it sounds the most neutral and idiomatic.

Could this also be said with truditi se, like On se trudi ne kihnuti na sastanku? Is there a nuance difference from pokušava?

Yes, that sentence is correct:

On se trudi ne kihnuti na sastanku.

Nuances:

pokušavati / pokušati – try, attempt (focus on the attempt itself)
truditi se – make an effort, exert oneself (focus a bit more on the effort, struggle)

In many contexts they can be interchangeable, but:

On pokušava ne kihnuti na sastanku.
He is trying (making an attempt) not to sneeze.
On se trudi ne kihnuti na sastanku.
He is putting effort into not sneezing (perhaps it’s quite hard for him).

Both sound natural; the difference is subtle.

If I want to say “He is trying not to cough at the meeting,” do I just replace kihnuti?

Yes, you keep the structure and replace the verb:

On pokušava ne kašljati na sastanku.
He is trying not to cough at the meeting.

Note: with coughing, the imperfective kašljati is usually more natural, because coughing is often a repeated/ongoing action. For a single cough you could use kašalj (noun) in other constructions, but for this pattern ne kašljati is what you want.