Can a rogue planet neither orbit around a star nor a galaxy? As we know, rogue planets don't orbit around a star, how about galaxy? Can a rouge planet not orbit around a galaxy?
They would be enormously difficult to observe, but with a big enough gravitational assist a rogue planet certainly could be ejected from a galaxy and become a "double rogue" so to speak, or intergalactic rogue planet is probably a better term.  Rogue (or intergalactic) stars have been observed.  Here and Here.  The same gravitational forces that create intergalactic stars absolutely should create inter-galactic rogue planets and in fairly significant numbers.  The merging of 2 galaxies should create millions of them.