Read the whole thing! Right below your red questions, it
tells you "where [v]
x is ..."! No, the brackets don't mean absolute value, and the subscript cross is a multiplication sign, but that doesn't really matter since the whole symbol is defined.
And, yes, ||v|| would be the magnitude, and I would be the identity matrix.
Not that I am at all familiar with what is being done here.
Also, it's helpful if you provide a
link when possible, in case context mattered (such as if the definition were given right after where you stopped.)