Are humans the only animals who know they're going to die?

Most likely, elephants, for example dig shallow graves for their dead, and many animals go to warm cozy places to die, whether they cognitively think about death is another thing, its highly probable all animals know they will die, but I do not think they really think about it much.

I think a lot of species of animals too know this as they too would have seen the death of the species of their kind and that of others too.

We're already dead.

He who is forgetful of the Self, mistaking the physical body for it, and goes through innumerable births, is like one who wanders all over the world in a dream. Thus, realizing the Self would only be like waking up from the dream­wanderings.

Sri Ramana Maharshi (December 30, 1879 – April 14, 1950)

Ps. 17:15

As for me, I will behold thy face in righteousness: I shall be satisfied, when I awake, with thy likeness.

“Sleep not"; "Awake, for you know not the hour"

George gurdjieff (September 26, 1898 – July 11, 1937) In reference to humans being Automatons:

They are not yet made in their Fullness they are just seeds rooted in heaven to grow back on earth in their Fullness, their Spiritual Likeness of G-D upon the earth. Ps.17:15. It is G-D Declare Decree: a Law to enter in His Dwelling Place G-D has prepared in the earth for the seed to enter in and return back in His Likeness in the earth.

The Children of G-D are gods that have Eternal Life the Breath of their Father G-D in them. They return to the House of Their Father like Abraham Gen.24:7 Isaac Gen.27:27 and Jacob Gen.28:20-21. Dust to dust, ashes to ashes and spirit to Spirit.

I don't know the answer but this question caught my attention! Keep me updated!

We don't really know that.