Nescio quid in foro fieri possit.

• Nescio: I do not know; 1st person singular present active indicative of nescire
• quid: what; neuter singular interrogative pronoun
• in: in
• foro: in the forum / marketplace; ablative singular of forum
• fieri: present passive infinitive of facere; here it can mean to be done or idiomatically to happen
• possit: may be able / can / may; 3rd person singular present subjunctive of posse

So the basic structure is I do not know + what + can happen / be done + in the forum.

Because quid in foro fieri possit is an indirect question after nescio.

Latin regularly uses the subjunctive in indirect questions:

• Scio quid faciat = I know what he is doing
• Rogo ubi sit = I ask where he is
• Nescio quid possit = I do not know what can happen

So possit is not subjunctive because the action is unreal; it is subjunctive because the clause is grammatically an embedded question.

Because this is a question word: what?

• quid is the neuter form of the interrogative pronoun
• quod is usually a relative pronoun or a conjunction

Here the sentence means I do not know what can happen, so Latin needs the interrogative form quid.

Because posse normally takes an infinitive.

So:

• possit = can / may
• fieri = to happen / to be done

Together:

• fieri possit = can happen or can be done

This works much like English:

• can happen
• may be done

Latin often builds this idea with a form of posse plus an infinitive.

Formally, fieri is the present passive infinitive of facere, so at its most literal it means to be done or to be made.

But in Latin, fieri is also very commonly used in the sense:

• to happen
• to come about
• to occur

So in this sentence, depending on context, you can understand quid in foro fieri possit as:

• what can be done in the forum
• what can happen in the forum

Both are grammatically possible; context tells you which nuance is intended.

Because in takes the ablative when it means location.

• in foro = in the forum
• ablative because the idea is where

Compare:

• in forum = into the forum
• accusative because the idea is motion toward

So here in foro answers where can it happen? and that requires the ablative.

In this sentence, quid is best understood as the thing that can happen or can be done.

With fieri in the sense to happen, quid functions like the subject of the idea:

• what can happen

With fieri in the more literal passive sense to be done, it is still the thing being spoken about:

• what can be done

A small detail that often confuses learners: in the neuter singular, the nominative and accusative forms are the same, so quid does not visibly distinguish those two cases here.

It may look unusual from an English point of view, but it is normal Latin.

Latin word order is much freer than English word order. The key relationships are shown more by endings and forms than by position.

This sentence is arranged as:

• Nescio = main verb first
• quid = introduces the indirect question
• in foro = location
• fieri possit = verbal idea at the end

A more English-like order might be:

• Nescio quid possit fieri in foro

That would mean essentially the same thing. Latin can move these parts around for emphasis or style.

Possit is present subjunctive.

Because the main verb nescio is present, Latin normally uses a present or perfect subjunctive in the indirect question according to the usual sequence of tenses. Here the present subjunctive is the natural choice.

In English, depending on context, you might translate it as:

• can
• may
• could

So the sense is not necessarily strictly present-time only. It often expresses an open possibility from the speaker's current point of view.

Yes. Nescio quid can sometimes become an idiomatic expression meaning something like:

• something or other
• a certain something
• I know not what

For example, a phrase like nescio quid dulce could mean some kind of sweetness or a certain sweet quality.

But in Nescio quid in foro fieri possit, the natural reading is an actual indirect question:

• I do not know what can happen in the forum

That is because quid is followed by a full clause with possit.

Yes, but the meaning would be a little different.

• quid in foro fiat = what is happening / what is being done in the forum, or in some contexts what may be happening
• quid in foro fieri possit = what can happen / what can be done in the forum

So fieri possit adds the idea of possibility or ability, not just simple occurrence.

In classical Latin, forum usually means a public square, marketplace, or civic center of a town.

So in foro means something like:

• in the marketplace
• in the public square
• in the forum

It does not originally mean an online discussion space; the English word ultimately comes from this Latin one.