In Crusader Kings 3, is there a way to determine the special building options?

The most common usage for that is slot is a Duchy Building, which can only be built in the Duchy Capital. Those should appear in the screen of your screenshot, so this is clearly not a Duchy Capital.

Special Buildings also use that slot. The Paradox wiki gives this list for where Special Buildings are possible:

Barony is a holy site
Barony is the site of a historical building
Barony is the site of a mine
Barony is the site of a university

The Paradox wiki also has a list for Duchy Buildings and a list of Special Buildings. See there for more details.

I'm not sure how to build those Special Buildings. The ones I had were pre-built. I recall a decision to build a University at some point, but didn't meet the requirements yet. And it was limited to the historical location of that University.

The wiki says this about Universities:

Unless already built, one can build a university through the "Found University" decision [..]

But the description is unclear on some of the other Special Buildings, so I can't rule out some can be built using the regular menu.

So to answer your question:

Is there an in game way of telling what options are available and how to unlock them?

Check the list of decisions available to you to see options beyond those available to you in the Buildings screen.