There are a number of different pickups for a banjo, but all of them will use a 1/4" jack that you plug your guitar cable into. On resonator banjos the jack is usually attached to the flange, but on openback banjos the most secure way of attaching the jack is through the side of the rim of the banjo.
To attach a pickup jack through the rim of your banjo you will need to drill a whole through the rim. You will need the following tools:
Watch the video below to see exactly how to do this.