A website specifically funded by the animal agriculture industry, with no relevant citations or studies, is your reference to whether animals know they are going to be slaughtered or not? "Based on research..." was the first sentence of the description, yet I did not hear any studies being cited, only stories about what she saw. Why should I trust her? She is biased and works in the industry, she's not going to say "oh yeah they suffer and die." Neither of the two studies at the bottom have anything to do with the question "do animals know they are going to be slaughtered". One is on bolt stunning and one is a paper by her on minimizing distractions, neither of which discusses the topic. If this is the best the animal industry has to prove animals don't know they are going to die, then I'm not buying.
As a side point, even if someone is unaware they are going to die, is it still okay to kill them? No.