Most bicycle trailers use a hitch that mounts under your rear axle nut. On our bikes, it's almost always easier to mount this on the left side, avoiding the shifting systems on the right.
The hub-drive bikes use a larger axle than standard, so most hitches will not fit on them. To install an axle-mounted trailer hitch on these bikes, remove the left side axle nut and anti-rotation washer (it's the teardrop-shaped piece under the nut) and then install this adapter:
Mount the hitch on the adapter and then install the axle nut to secure the hitch.