Can college professor give you a negative grade?

There's no grade lower than 0, and a college prof can definitely give you a 0 on an assignment if you don't do the assignment or take an exam.

You're an adult now and nobody's going to lead you by the hand.  it's your responsibility to read all the information given to you by your profs and to follow up on it.  

I wouldn't tell that prof you didn't show up because you didn't know you had to.  He's not going to care and it's not going to raise his opinion of you as a student.

Yes.  The professor can deduct points from your overall grade for missing presentations.  Not paying attention to the assignment details is not an excuse -- it is merely the reason you didn't do what was required. 

I'd contact the professor ASAP and look into dropping the class if you're likely to get a grade below a C.  Grades of D and F (and even C) can seriously damage your GPA.  You might be better off taking a "W" and retaking the course with greater attention to detail and focus. 

He'll actually *believe* the excuse that you didn't know, all right! He just won't care. You're responsible for reading the syllabus, including all assignments, due dates, and requirements. 

He probably can't or won't give you a grade below 0 for the assignment.

That said, failing to complete even a single assignment might allow him to drop you or fail you, in an online class. Last semester I was getting an A in a class, and decided to blow off a small assignment that was 1. impossible to complete, since it involved getting in touch with a former volunteer supervisor, at an organization that had closed due to Covid, and 2. worth like 1% of my grade total grade. Man, you've never seen such a fuss. I nearly flunked a class in which I had a 98% average. They did, eventually, let me out of the assignment, but they had to change it to "not required"; I couldn't just take the 0 and move on. 

That boils down to you need to do the presentation, even if you're still just getting a 0 for it.

And you never know; he might be generous. Lots of professors' barks are worse than their bites.

I would like to be there when you tell an employer that you didn't show up for work because you failed to look at the schedule. This is totally your responsibility. I know professors who wear a shirt to class that says "It's in the syllabus" and give quizzes on the syllabus to try to get students to actually read it! You'll find that your life will be better and more successful if you just pay attention to things. 

I doubt if he will give you a negative grade, but if it is consistent with his gradring rules then he could.

I think it's most likely you will get a 0 on the assignment and not a -40.  The fact that you didn't know is certainly believable, but it's not excusable.  As you said, it was written in the assignment instructions/requirements and it's your responsibility to stay on top of those types of things.