So in the rental im at right now I have an old Directv pole mounted to the roof. The dish isnt there. Just the pole. Is it possible to mount my antenna to this? If so, what type of mount bracket would I need?
With a antenna of any size, you will find that the J pole mount will not work because it's foot print is too small.
Your best bet is to buy a antenna mount kit and put the antenna on the side of the house.
Since you did not say what kind of antenna you wanted to mount, and you are there and I am here, it is hard for me to suggest what you need.