Is Non Dual Vedanta's Brahman aware of itself, if so isn't it he same as Trika Shavism, and can there really be any difference in Non Dual philosophies e.g. Buddhism, Advaita Vedanta, Kashmir Shaivism?
Nondual Brahman is Pure Consciousness or awareness itself. One can't say anything more than this. The question whether non-dual Brahman is aware of itself cannot be answered. One has to remain silent to this type of question.
The Upanishad also declares Brahman to be Consciousness alone. The Upanishad also says that Brahman is pure consciousness, devoid of other aspects contrary to this, and without any distinguishing features, as in, “As a lump of salt is without interior or exterior, entire, and purely saline in taste, even so is the Self without interior or exterior, entire, and pure Intelligence alone” (Brhadaranyaka Upanishad IV.v.13), which means that the Self has no internal or external aspect apart from pure consciousness, Its nature being mere impartite consciousness without any interstices. Just as a lump of salt has the saline taste alone both inside and outside, and no other taste, so also is this Self.
Brahma Sutra Bhasya of Sri Sankaracharya III.ii.16
Moreover, the Vedas reveal this; likewise this is mentioned in the Smritis also.Moreover, the Vedas reveal through a negation of other aspects that Brahman has no distinguishing feature, as for instance in, “Now therefore the description (of Brahman): ‘Not this, not this’” (Brhadaranyaka Upanishad II.iii.6), “That (Brahman) is surely different from the known; and, again, It is above the unknown” (Kena Upanishad I.4), “That Bliss of Brahman, failing to reach which, words turn back along with the mind” (Taittiriya Upanishad II.ix.1), and so on. And it is also known from the Vedic texts that Badhva being asked by Baskali, replied merely by not uttering a word, as stated in, “He (Baskali) said, ‘Teach me Brahman, sir.’ He (Badhva) became silent. When the question was repeated a second and a third time he said, ‘I have already spoken, but you cannot comprehend. That Self is Quiescence’ “. Similarly in the Smritis, the instruction is given through a negation of other things, as in, “I shall tell you of that which is to be known and by knowing which one attains immortality. The supreme Brahman is without any beginning. It can neither be called gross (visible) nor fine (invisible)” (Gita XIII.12), and so on. Similarly the Smriti mentions how Narayana in His cosmic form said to Narada, “O Narada, that you see me as possessed of all the (five divine) qualities of all elements, is only because of My Maya, called up by Myself. For else you should not understand Me thus.”
Brahma Sutra Bhasya of Sri Sankaracharya III.ii.17
Advaita non-dual Brahman is ontological. Such a Brahman really exists and is not just a mental phenomenon. Buddhist non-duality is psychological, i.e., it is a mental state. Mind, of course, stops during the experience of non-dual Brahman according to Advaita. I would think that Kashmir Saivism concept of Siva would be closer to Advaita than Buddhism.