Is this argument valid?
Therefore
What I think, is that is impossible to know, because we don't know if the second premise is true or false, so the only thing we can do is to check if it is logically valid, which in that case, the conclusion is going to be false.
The argument is valid in the sense that anyone who accepts the premises ought to accept the conclusion too -- it is logically incoherent to reject the conclusion while accepting the premises.
Or is it? One may object that there is a hidden assumption that consciousness exists (and has external manifestations) in the first place. Without this assumption the two explicit premises do not actually force us to conclude that there is a physical phenomenon that cannot be simulated.
Descartes could convince himself that consciousness exists by introspection, but that doesn't count in logic. I can certainly imagine a world that contains no conscious beings, and which is completely simulable. In such a world both of the premises here would be vacuously true, which invalidates the argument, because a valid argument ought to be valid for all imaginable worlds, not merely for worlds that happen to contain me.
Exercises like this are most often found in the very early pages of textbooks in mathematical logic. They're generally intended to drive home the point that one can determine the validity of an inference without committing to an opinion about whether the premises and/or conclusion are actually true.
In this case it can also be used as a motivation for discussing whether accepting the claims "all As are Bs" necessarily also means you accept that there must be any As in the first place. The ancients, most importantly Aristotle, said yes; modern mathematical logic generally says no.
How much these exercises actually help anyone is a good question -- I am somewhat skeptical.
