For an assignment I’m trying to find a word that describes a particular feeling. I’m not sure what word describes the feeling of not knowing WHAT is going to happen but still expecting something to happen at the same time.
The specific sense of something bad about to happen is called forboding.
a prediction; portent.
a strong inner feeling or notion of a future misfortune, evil, etc.; presentiment.
"He woke that morning with a sense of forboding that lingered until he received the phone call about his friend's sudden death."
The words below allow the object of the feeling to be unknown, but also, and perhaps more commonly, allow for it to be known.
The following two are exclusively used for unpleasant feelings.
Fearful apprehension; a feeling that something bad will happen.
with a sense of foreboding she read the note
Anxiety or fear that something bad or unpleasant will happen
There were a lot of apprehensions about the future
Most of the rest of them can be used to describe a good feeling, though they are more commonly used to describe a bad feeling:
A strong feeling that something is about to happen, especially something unpleasant.
anticipation of an event without conscious reason (Merriam-Webster)
I had strong premonitions of doom, the unmistakable feeling I was walking into a trap.
An intuitive feeling about the future, especially one of foreboding.
Immediately she had shut her eyes sensing some peculiar presentiment
(In this sense, archaic) A feeling of presentiment or foreboding
Terrified by her presage of death, the patient immediately contacted Mitchell for a series of consultations.
There is one that is mostly used to describe positive feelings, although it is sometimes used to describe bad ones:
anticipation The action of anticipating something; expectation or prediction.
the act of looking forward; especially, pleasurable expectation (Merriam-Webster)
The act of expecting or foreseeing something; expectation or presentiment (American Heritage)
None are happy but by the anticipation of change: the change itself is nothing
That could well be a gut-feeling: TFD
an intuition or instinct, as opposed to an opinion based on a logical analysis.
He had a gut feeling that something bad is going to happen.