To be

JumanahIt means "the girl supposed, going, or must..."

I don't know what you mean by that,

For example, "The girl to be told about that is here" can mean
"The girl who must be told about that is here", "the girl who is going to be told...", or "the girl who is supposed.."
Is that correct?
And is it correct to say "The girl supposed to be told about is here"?

JumanahAnd is it correct to say "The girl supposed to be told about is here"?

No.

"About" needs an object.
The sentence is awkward.

JumanahFor example, "The girl to be told about that is here"

The girl who must be told about that is here.
The girl who is going to be told about that is here.
The girl wh

What about these?
"It's the final exam to be given to the students" can mean
It's the final test that must be given..." , "it's the final test that going to be given...: or "it's the final exam that is supposed..."
Is that correct?

"It's the final exam to be given to the students.

The closest in meaning is:

It's the final test that is going to be given to the students.

Is it correct to say "She's the only one going there tomorrow"

But I think it can in some cases mean "must" or "supposed"
Am I right?

JumanahIs it correct to say "She's the only one going there tomorrow."

Yes. No one else is going.

JumanahBut I think it can in some cases mean "must" or "supposed"

Well, we usually say what we mean. If we meant "must" or "supposed", we would say those words.

Is this the test we are supposed to give the students tomorrow?