If you can use a dial test indicator (clock gauge) or know an engineer that can, set it on the wheel rim and pull/push the wheel to measure the play. Its a millimetre maximum sideplay allowed at the rim but you will feel any play in your hands from the bearing long before it reaches that.
Same goes for the swingarm bearings and the paralevel/bevel knuckle, you can feel that in your hands and see the flex in it when it is worn. All these little bits of wear and tear add up the further down the bike you go so by the time you get to the rear wheel it feels massive when its actually very little.
Another thing worth checking is the long but slender frame bolt under the right hand rear side of the gearbox above the catalyst. It vibrated out on my first 2004 1200GS and the bike flexed slightly like it had a hinge in the middle, solved with buying a new bolt plus a dab of loctite.