It is questionable whether the concept of identity applies to whatever it is that is the experiencing. It is only of two objects existing in the context of a topologically structured world, that is a world where they can have some sort of boundaries and where their separation, e.g. in time or space or both, makes sense, that the question arises as to whether they are the same or different. Putting aside the question of what distinguishes this person here from that person over there, that is of two subjectivities, it is necessary to begin with the question of whether there can be one subjectivity. Here nothing in respect of the contents of experience, whether in terms of furniture of the world or of thoughts or qualia can do the trick. The former are at best cut off from the exeriencing of them, are transcendences too far away to serve as witnesses (the object may have identity but it can't pass that on to you by virtue of your experience of it - and its experience of you is not evident) and the latter are too fleeting, they merely arise and pass, and rather quickly at that, and bear only a formal resemblance among themselves. No, you would have to say something like, 'it is the screen on which experiences appear that is identical.' But how could you know this, apart from the contents appearing on the screen which have already been ruled out? Anyway, there is no evidence that there is such a screen, it's only a way of speaking. When you say 'the experiencing' it is just a way of trying to point to that which can't be pointed at, metaphorically the eye or 'I' that is looking at the 'screen'. And here you could say that there is no room for any criterion of identity - 'it' is just too small, or too large. As to the question of an alter-subject, this is so far downstream of the experiencing as to again make the question of 'same or different?' absurd.