What is the possibility that a portion of the earths centre or another planet having a super dense magnetic allotrope of Hydrogen?

it's called metallic hydrogen.

earth, no. lol. earth's iron-nickel core is well-established.

jupiter? almost certainly. saturn? maybe.

Not Earth.
Jupiter might have an area of 'metallic' hydrogen - Hydrogen packed so dense that it can be thought of as a solid; but, differentiation within Earth would've replaced hydrogen in the core with iron, nickel, and other heavy elements.