So where is the best place to place the jacks in order to lift the trailer to remove a wheel or work on the bearings?
Everyone has their favorite method of jacking a trailer for that purpose.
I use a 12 ton shorty hyd bottle jack that slides under the axle with leaf springs next to the U bolt. The jack is a truckers special made for that purpose. It came with a 6" long channel that is adapted to the jack which cradles the axle tube and eliminate the axle slipping of the jack. The jack simply raises the end of the axle (1500-3000 lbs) instead of the whole side of the trailer.
What ever method you choose make a dry run at home. Over the years I've seen and heard several people say the ramp device they bought for that purpose didn't lift thew flat tire.