This month's Trailer Life magazine had a good article on how to inspect the bearings and brakes.
Also, in NY State, most shops don't do it, but they are technically supposed to pull one wheel as part of the annual inspection and the state caps the price at something like $6 for trailer inspections (so auto shops hate doing them). I took ours to the dealer for the inspection and watched the tech pull the wheel. Since he was a full time RV mechanic, it was a cheap way to get a professional opinion on the condition of the brakes and bearings. He said good to go - consider re-packing the bearings next year.