Conciousness in Buddhism and Advaita Vedanta I would be happy if someone could clear up a doubt for me.

When Advaita talk about consciousness without boundaries it is said to be the "Self". It is described as combining being and knowing in one thing. This being and knowing divides itself in two, and becomes the knower (subject) and the known (object), which creates the duality. Now when the knower-and-the-known duality has been eradicated, it is said that what remains is this knowing-being self.

Now I am confused because I heard that somewhere in the Canon the Buddha talked about the conciousness vinjana without boundaries that the Arahat have.

Is he talking about the knowing-being self that the Advaita is talking about? And what exactly is this consciousness that the Buddha talks about: is it the same as knowing-being that Advaita talks about, when the duality of self and not-self has been removed?

I read somewhere that Buddhism says that knowing-being is not true: because consciousness always consciousness-of-something, in other words it cannot be conscious-of-itself, and therefore consciousness-of-itself or knowing-being as one thing is not possible. Please clarify this for me so that I understand, thanks.
In (Mahayana) Buddhism we say something similar, but a Buddhist description tries to be a little more careful and nuanced.

We say that vijnana ("consciousness", "experience") is always dualistic, always split into subject/object and object/background. And, we also say that vijnana is not a "something", it's a process, not an entity, so to say that "it" can or cannot be conscious of "itself" is silly. The process of cognizing can only cognize memories or thoughts about the process of cognizing.

We say that this dualistic or "tainted" process of vijnana develops from tendencies for liking and disliking, according to process known as Dependent Origination. And that before this development occurs, there's a state of great nondifferentiation. This nondifferentiation is not necessarily good or bad, after all it carries potential for developing into confusion of Samsara, but it also carries potential for developing into the Buddha. What this nondifferentiation tells us is that all boundaries and all dualities are mind-made, and that therefore all our troubles lie within those mind-made frameworks, the troubles only have their existence within those conceptual frameworks. 

Finally, we recognize that someone may attain a first-hand realization of how all of this works and see these mind-making processes directly as they happen in real-time. Someone like that would see both, all mind-made boundaries and frameworks, all dualities of "this" vs "that" - but also at the same time see "the ground" of all of these, the reality underlying differentiation. We call such vision "enlightenment" and such person "a buddha".

When this enlightenment is attained, it involves seeing beyond all dualities, including duality of "me" vs "world". It becomes clear that mind has no boundaries. This mind (rigpa) is not the same as the process of dualistic cognition that we call consciousness or vijnana, but something much more fundamental, it is the fundamental principle of information exchange. Mind is inherently luminous because it is the very capability of representation. Mind is everywhere and flows everywhere because everything carries some representation, so in some sense everything is mind.

This is very similar to what they say in Advaita Vedanta, however there is an important difference. We don't say that mind is "I" or "self". It seems silly to equate the (ever-dualistic) subject with the fundamental principle beyond subject-object duality. Calling it "I" makes it seem like it is the same as our own self-awareness, and that therefore our individual self-awareness will somehow last forever, which is not true. Mind is not the subject, it's not the universe, it is the fundamental principle, the fundamental law giving the rise to both the subject and the universe. In Buddhism we don't say "I am the law" :))

Instead, we study this Law in all its aspects - as mind, as Depenent Origination, as self-perpetuating accumulation of tendencies, as Being-Time (see Dogen), as the source of Samsara and Nirvana, as Emptiness, as karma, as Three Marks of Existence  - and we take comfort in knowing that this Law is one thing that is not subject to impermanence and is therefore something we can finally rely on. 

We also don't say that mind is something special or fundamentally different from everything else. So it's not like this mind is One Aware Entity watching everything in the universe, no - mind is just an aspect of how everything works, part of everyday things.

To summarize, in Mahayana we agree with idea of nonduality of Being and Mind, but we are careful to not confuse it with such dualistic concepts as "I", "consciousness", and "the universe".